CMU Block Calculator
CMU block calculator for concrete, cinder, and cement block walls. Enter wall size to get blocks, mortar bags, sand, and grout needed, with cost.
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How the CMU Block Calculator Formula Works
Start with the wall's net area: length times height, minus any door or window openings, since blocks don't get laid where an opening sits. A standard 8×8×16 inch concrete block has an actual size of 7-5/8 × 7-5/8 × 15-5/8 inches; with a standard 3/8 inch mortar joint added on each side, it occupies a full 8×16 inch nominal footprint on the wall face, which is 128 square inches, or 0.889 square feet. Dividing the net wall area by 0.889 square feet, equivalently multiplying by 1.125, gives the raw block count, and a waste percentage is added on top for cuts and breakage.
Mortar coverage, meaning how many blocks one bag lays, depends on what is actually in the bag, so it is an editable input rather than a fixed constant. The default is 30 blocks per 70 lb bag of masonry cement, the Concrete Masonry & Hardscapes Association's published figure. Masonry cement is mixed with sand on site, which is why sand is estimated separately. Pre-blended mortar mix already has the sand in the bag, so a 60 to 80 lb bag lays far fewer blocks, roughly 9 to 15 depending on bag size and who is quoting it. The published figures differ mainly because they describe different products. Enter the coverage for the bag you are actually buying. Sand follows the bag count at 1 ton per 8 bags of masonry cement, per the same CMHA source, so skip the sand line if you use pre-blended mix.
Grout core-fill, when the wall's cores will be filled solid, is estimated from roughly a quarter cubic foot of grout per standard 8 inch block, scaled up or down for wider or narrower block since a wider block has a larger hollow core to fill.
blocks = ceil((wallLength*wallHeight − openingsArea) * 1.125 * (1 + waste%)); mortarBags = ceil(blocks / blocksPerMortarBag); sandTons = mortarBags / 8; groutYd3 = includeGrout ? blocks * (0.25 * blockWidth/8) / 27 : 0- wallLengthft20The finished wall's total length.
- wallHeightft8The finished wall's total height.
- openingsAreaft²0Combined area of doors, windows, and vents cut into the wall, subtracted before blocks are counted.
- blockWidthin8Block thickness: 6, 8, 10, or 12 inches. The block's face (and so the blocks-per-square-foot figure) stays the same standard 8×16 inches regardless of width; width changes only the grout core-fill volume.
- wastePercent%5Extra blocks added for cuts, breakage, and layout waste, on top of the raw block count.
- + 3 more inputs below
- wallLength
- ft
- The finished wall's total length.
- wallHeight
- ft
- The finished wall's total height.
- openingsArea
- ft²
- Combined area of doors, windows, and vents cut into the wall, subtracted before blocks are counted.
- blockWidth
- in
- Block thickness: 6, 8, 10, or 12 inches. The block's face (and so the blocks-per-square-foot figure) stays the same standard 8×16 inches regardless of width; width changes only the grout core-fill volume.
- wastePercent
- %
- Extra blocks added for cuts, breakage, and layout waste, on top of the raw block count.
- blocksPerMortarBag
- blocks/bag
- How many blocks one bag lays. Defaults to 30 for a 70 lb bag of masonry cement (CMHA's published figure, sand added separately). Pre-blended mortar mix, with sand already in the bag, lays far fewer per bag, roughly 9 to 15 for a 60 to 80 lb bag, so change this to match the product you are buying.
- includeGroutFill
- n/a
- Turns on the grout core-fill estimate for a solid-grouted wall.
- pricePerBlock
- $
- What your supplier quotes per block, for a total material cost estimate.
Using the CMU Block Calculator
Enter wall lengthft
Type the figure you already have, then press Calculate.
Enter wall heightft
Type the figure you already have, then press Calculate.
Enter doors, windows & openingsft²
Type the figure you already have, then press Calculate.
Enter block width
Choose from 6 inch, 8 inch (standard), 10 inch, 12 inch.
Enter waste allowance%
Type the figure you already have, then press Calculate.
Enter blocks laid per mortar bag (70 lb)blocks/bag
Type the figure you already have, then press Calculate.
Enter solid-grout the cores
Switch this on or off depending on which applies to you. This one is optional.
Enter price per block$
Type the figure you already have, then press Calculate.
Read the result
Press Calculate to update the result. Until you do, the last result is dimmed and marked as out of date, so you always know which numbers belong to the values in the boxes.
A Real Worked Example
A 20 foot long, 8 foot high wall with no openings is 160 square feet. At 1.125 standard 8×8×16 blocks per square foot, that's 180 raw blocks; adding a 5% waste allowance brings it to 189 blocks after rounding up, since a partial block still means buying a whole one.
Mortar uses the default coverage rate of 30 blocks per 70 lb bag (CMHA's published figure): 189 / 30 rounds up to 7 bags. Sand follows at 1 ton per 8 bags of mortar cement, so 7 bags needs 0.875 tons. At $1.75 per block, the 189 blocks alone come to $330.75 before mortar, sand, and labor are added in. No grout core-fill is included here since this wall isn't being solid-grouted.
Wall with a door opening, 12 inch block, solid-grouted
A 12 by 8 foot wall is 96 square feet gross, but a 20 square foot door opening (a standard 3 foot by roughly 6 foot 8 inch door) brings the net area laid in block down to 76 square feet. At 1.125 blocks per square foot plus 5% waste, that's 90 blocks after rounding up, noticeably fewer than the primary example despite a similar footprint, entirely because of the opening.
Mortar needs only 3 bags for this smaller block count (90 / 30, no rounding needed), and 0.375 tons of sand. Because this wall uses 12 inch block and the cores are being solid-grouted, the grout estimate scales up from the 8 inch baseline by width (0.25 × 12/8 = 0.375 cubic feet per block), coming to 1.25 cubic yards for all 90 blocks. At $2.10 per block, the block cost alone is $189.00.
Same wall with pre-blended mortar mix (about 14 blocks per bag)
Same 20 by 8 foot wall as the primary example, but buying pre-blended mortar mix instead of masonry cement, so the coverage is set to about 14.3 blocks per bag, within the 9 to 15 range quoted for 60 to 80 lb bags of mix. Block count and cost don't change, since mortar coverage has no effect on how many blocks the wall needs, but the mortar bag count doubles from 7 to 14. The sand figure of 1.75 tons shown alongside only applies to masonry cement mixed on site; with pre-blended mix the sand is already in the bag, so that line should be ignored. The point of the example is that the same wall needs very different bag counts depending on the product, which is why coverage is a field you set rather than a fixed number.
A 10 × 12 ft shed on a 4 ft block foundation
A 10 by 12 foot shed has a perimeter of 44 feet. At 4 feet high, which is 6 courses of 8 inch block, the walls cover 176 square feet. At 1.125 blocks per square foot plus 5% waste, that is 208 blocks, enough for 7 bags of mortar at 30 blocks per bag and 0.875 tons of sand.
A shed foundation usually leaves a gap for a door or vents, so subtract that area in the openings field if you plan one. Check footing and frost depth requirements with your local building department before you order, since those decide how many courses go below grade.
A 1,000 square foot wall, 100 ft long and 10 ft high
A 100 foot long wall at 10 feet high covers 1,000 square feet. The raw count is 1,125 blocks and 5% waste brings the order to 1,182. Mortar at 30 blocks per bag is 40 bags with 5 tons of sand.
If you buy a pre-blended 80 lb mix that lays about 13 blocks per bag, the same wall needs 91 bags instead, which is why the bag you buy matters more than the wall size when you are budgeting mortar. At 90 blocks per pallet, 1,182 blocks is 14 pallets.
A 30 ft garden wall, 4 ft high, at a quoted block price
A 30 foot garden wall at 4 feet high is 120 square feet, which needs 142 blocks with 5% waste, 5 bags of mortar and 0.625 tons of sand. At a quoted price of $2.50 per block, the blocks come to $355.
The quote above is an example figure, not a market price. Enter the price you were actually quoted, and add the cap blocks, footing concrete and delivery separately.
What Else to Know
Standard CMU Sizes and What Each One Is Actually Used For
Every standard concrete masonry unit shares the same 8×16 inch nominal face, whether it's a thin 4 inch partition block or a heavy 12 inch structural block. Width is the one dimension that actually varies by use. ASTM C90, the governing US specification, sets the real (as-manufactured) size 3/8 inch smaller than the nominal size in every direction, so a nominal 8×8×16 block's actual dimensions are 7-5/8 × 7-5/8 × 15-5/8 inches; the surrounding 3/8 inch mortar joint fills the gap back out to a clean 8-inch grid, which is why courses of block line up cleanly with other 4-inch and 8-inch building materials.
6 inch block shows up mainly on non-load-bearing partition walls and some garden or landscape walls, where full structural width isn't needed and the narrower block saves material and interior space. 8 inch is the default for most residential and light-commercial load-bearing walls, foundation walls, and retaining walls, which is why it's the default width on this calculator and in nearly every competing one. 10 and 12 inch block step up for taller retaining walls, foundation walls carrying heavier loads, and some fire-rated or sound-rated commercial assemblies, where the extra width buys more load capacity and a larger grout-filled core.
Because the face stays 8×16 inches at every width, the blocks-per-square-foot math above (1.125 blocks per square foot) doesn't change when width changes. Only the grout core-fill volume does, since a wider block has more hollow core to fill.
Mortar and Sand: Which Bag You Buy Changes the Math
Mortar coverage is the number that varies most between block estimates, and the reason is mostly the product in the bag. Masonry cement is sold without sand and mixed with sand on site; the Concrete Masonry & Hardscapes Association's published guidance (TEK 04-02A) says one 70 lb bag lays roughly 30 standard blocks, about 3.3 bags per 100 blocks. That is the default here. A 94 lb bag of straight portland cement, used in a portland cement-lime mix, lays roughly 62 blocks instead, because it is a different product with a different yield.
Pre-blended mortar mix is the other common choice, and it already has the sand in the bag, so each bag makes less mortar for its weight. Figures quoted for 60 to 80 lb bags of pre-blended mix run from about 9 to 15 blocks per bag, which means the same wall needs roughly two to three times as many bags. The additional worked example above runs the identical wall at 14.3 blocks per bag to show it: blocks and cost stay the same, bags double from 7 to 14. Neither number is wrong; they describe different bags. That is why coverage is a field you set yourself ("Blocks laid per mortar bag" above) instead of a constant buried in the formula.
Sand follows the bag count at 1 ton per 8 bags of masonry cement, per the same CMHA source, which works out to about 240 blocks per ton of sand. That line only applies when you buy masonry cement; with pre-blended mix the sand is already in the bag, so skip it. Both approaches assume standard 3/8 inch joints and face-shell bedding, meaning mortar on the block's outer shells rather than filling the hollow core. Actual coverage still varies with joint thickness and mason technique, so treat either figure as a planning number to order against rather than a guarantee.
Grout Core-Fill: When You Need It and How Much
Most concrete block walls are never fully grouted. Mortar on the face shells alone is structurally sufficient for a typical residential or light-commercial load-bearing wall. Solid grouting, filling every hollow core with poured grout, shows up specifically where the wall needs extra strength or a continuous concrete core: reinforced walls with vertical rebar running through the cores (the grout bonds the steel to the block), foundation and below-grade walls carrying more lateral soil pressure, and taller retaining walls where added mass and strength matter more than material savings.
The core-fill estimate here starts from roughly a quarter cubic foot of grout per standard 8 inch block, a commonly cited figure for a typical hollow-core unit, and scales that proportionally for wider or narrower block, since core volume grows with block width while the shell thickness around it stays roughly similar. Treat this as an engineering approximation rather than a fixed trade constant the way the mortar and sand figures are. Actual core volume varies by manufacturer and block design, so a supplier's own published core-fill volume for your specific block is worth checking against this estimate before ordering a full truckload of grout.
When only some cores are being grouted (around rebar only, say, rather than every core), this calculator's full-wall grout estimate will overstate what's actually needed; it's built for a fully solid-grouted wall specifically. If the wall sits on a compacted base, the gravel calculator and stone calculator size that layer.
Coursing: Turning Wall Height into Courses and Blocks per Course
A block course is 8 inches tall on paper (7⅝ inches of block plus a ⅜ inch mortar joint), so every foot of wall height is 1.5 courses and every foot of wall length is 0.75 blocks. That is the same 1.125 blocks per square foot the calculator uses, just broken into rows. Counting courses is the quickest check on any estimate: an 8 foot wall is 12 courses, and if the wall is 20 feet long each course is 15 blocks, so the wall is 180 blocks before waste.
Heights that are not a multiple of 8 inches are where estimates drift. A 3 foot wall is 4½ courses, which in practice means either 4 courses (32 inches) or 5 courses (40 inches), with the last course cut or the footing adjusted. The coursing chart below lists heights that land on whole courses. Wall lengths have the same issue horizontally: a length that is not a multiple of 16 inches ends in a cut block, and a half block at a corner or opening is a normal part of running bond, not extra waste you can avoid.
The 5% waste default covers ordinary breakage and cuts. Increase it toward 10% for walls with many openings, short return walls, or work done in cold or rough conditions, and read the quantity the calculator gives as a purchase number, not a count of blocks that end up in the wall.
Mortar Types and Mix Ratios: M, S, N and Pre-Blended Bags
ASTM C270 defines four mortar types, M, S, N and O, by strength. For block walls, Types M, S and N are the ones building codes usually call for. Type S is the common choice for load-bearing walls, foundation walls and anything resisting side pressure from soil or wind. Type N suits above-grade, non-structural or lightly loaded walls. Type M is the strongest and is used where a wall is below grade or carries heavy loads. CMHA notes that empirical design of foundation walls requires Type M or S.
Mixed on site from portland cement, lime and sand, the proportions are by volume. The sand in each mix is measured in a damp, loose condition and must fall between 2¼ and 3 times the combined volume of the cement and lime. The table below shows each type at the top of that sand range, which is how the common batch recipes are written. A pre-blended mortar mix already contains sand, so you buy it by the bag and follow the label, not the ratio.
The bag you choose changes the count more than the type does. CMHA's guide of about 30 blocks per 70 lb bag assumes masonry cement with sand added on site. A sanded 80 lb Type S mix lays about 13 standard 8×8×16 blocks, according to the manufacturer's data sheet. Set the blocks-per-bag field to the number printed on the bag you are actually buying.
Block Weight, Pallets, and Moving the Load
Block weight depends on the concrete density, and the weight of a finished wall depends on how many cores are grouted. CMHA publishes wall weights per square foot for an 8 inch single wythe wall: an ungrouted hollow wall runs from 24 pounds per square foot for 85 pcf lightweight units up to 39 pounds per square foot for 145 pcf units. With 1.125 blocks in each square foot, that is roughly 21 to 35 pounds for each block including its share of the mortar. Solid grouting more than doubles the figure, which matters when you are deciding what a slab, truck or scaffold has to carry.
Blocks are sold on pallets, and the count per pallet depends on the block size and type. Standard 8×8×16 blocks are commonly listed at 90 per pallet, though yards quote anything from the low 70s to over 100 depending on the unit, so confirm the count when you order. The pallet table below divides a few common block totals by 90, then rounds up. Buy whole pallets only if the yard sells that way, since many yards will sell by the piece and take back full unbroken pallets.
Plan the delivery as well as the quantity. A pallet of 8 inch block weighs well over a ton, so the drop point, the ground it is set on and the distance to the wall are worth settling before the truck arrives.
Bond Beams, Running Bond, and Block Wall Types
Most block walls are laid in running bond, where each course is offset by half a block so the vertical joints do not line up. CMHA defines running bond as courses offset at least one quarter of the unit length, with centered head joints the most common form. It is the pattern the 1.125 blocks per square foot figure assumes. Stack bond, with joints lined up, looks different and needs horizontal reinforcement to behave structurally, but it uses the same block count per area.
A bond beam is a grouted course, reinforced with horizontal bars, that ties a wall together. Bond beam blocks have depressed or knock-out webs so the steel and grout can run through them. If your design calls for them, count them separately because they replace regular blocks in those courses and add grout. The calculator's grout figure assumes every core is filled, so it overstates grout for a wall that is only grouted at bond beams and rebar cells.
Wall type changes what you need besides the block count. A garden or screen wall is often 6 or 8 inch block, mortared and capped. A retaining wall needs a footing, drainage, reinforcement and usually engineered design. A structural wall carries load through its cores, so the grout and rebar are part of the design, not an option. For anything that holds back soil or supports a roof, the blocks are the easy part of the estimate. Ask your local building department what is required.
Concrete Block, Brick, or Poured Concrete?
Block, brick and poured concrete each win on a different job. A standard block face covers about 0.89 square feet, so a block wall goes up faster than brick, and one 80 lb bag of mortar mix lays about 13 blocks or about 37 standard bricks, so brick uses much more mortar for the same area. Block is also hollow, which lets you add rebar and grout where strength is needed instead of everywhere.
Poured concrete avoids joints but needs forms, bracing and a pour that cannot wait, which is hard to justify on a small wall. Block can be laid a few courses at a time, stopped for rain and finished by one or two people. Brick is usually chosen for appearance, either as a full wall or as a veneer over block, and a veneer wall is estimated as two separate materials.
Cost comparisons depend on local labor and material prices, so price all the options for your own wall instead of trusting a rule of thumb. The comparison table below lists the practical differences, and the calculator's price field turns any block quote into a total.
Reference Tables
| Nominal width | Actual width | Typical use |
|---|---|---|
| 4 in | 3-5/8 in | Non-load-bearing partitions |
| 6 in | 5-5/8 in | Partitions, light garden walls |
| 8 in | 7-5/8 in | Standard load-bearing walls, foundations |
| 10 in | 9-5/8 in | Taller retaining walls, heavier loads |
| 12 in | 11-5/8 in | Tall retaining/foundation walls, fire-rated assemblies |
| Wall size | Net area | Blocks | Mortar bags | Sand |
|---|---|---|---|---|
| 10 × 8 ft | 80 ft² | 95 | 4 | 0.500 tons |
| 20 × 8 ft | 160 ft² | 189 | 7 | 0.875 tons |
| 30 × 8 ft | 240 ft² | 284 | 10 | 1.250 tons |
| 40 × 8 ft | 320 ft² | 378 | 13 | 1.625 tons |
| Wall height | Courses | Blocks per 10 ft of length | Blocks per 20 ft of length |
|---|---|---|---|
| 2 ft 8 in | 4 | 30 | 60 |
| 4 ft | 6 | 45 | 90 |
| 5 ft 4 in | 8 | 60 | 120 |
| 6 ft 8 in | 10 | 75 | 150 |
| 8 ft | 12 | 90 | 180 |
| 10 ft 8 in | 16 | 120 | 240 |
| 12 ft | 18 | 135 | 270 |
| Wall length | Blocks per course | Wall length | Blocks per course |
|---|---|---|---|
| 4 ft | 3 | 20 ft | 15 |
| 8 ft | 6 | 24 ft | 18 |
| 10 ft | 7.5 (7 whole, 1 half) | 32 ft | 24 |
| 12 ft | 9 | 40 ft | 30 |
| 16 ft | 12 | 100 ft | 75 |
| Waste | Blocks | Mortar bags at 30 blocks per bag | Mortar bags at 13 blocks per bag |
|---|---|---|---|
| 0% | 113 | 4 | 9 |
| 5% | 119 | 4 | 10 |
| 10% | 124 | 5 | 10 |
| 15% | 130 | 5 | 10 |
| Blocks per bag | Bags for 1,000 blocks |
|---|---|
| 30 | 34 |
| 15 | 67 |
| 14 | 72 |
| 13 | 77 |
| 12 | 84 |
| Type | Cement : lime : sand | Typical use |
|---|---|---|
| M | 1 : ¼ : 3¾ | Below grade, foundations, retaining walls, heavy loads |
| S | 1 : ½ : 4½ | Load-bearing walls and walls resisting soil or wind pressure |
| N | 1 : 1 : 6 | Above-grade walls with light or moderate loads |
| O | 1 : 2 : 9 | Interior, non-loadbearing walls |
| Wall construction | 85 pcf | 105 pcf | 125 pcf | 145 pcf | 160 ft² wall at 125 pcf |
|---|---|---|---|---|---|
| Hollow, no grout | 24 | 29 | 34 | 39 | 5,440 lb |
| Grouted every 48 in. | 32 | 37 | 42 | 47 | 6,720 lb |
| Grouted every 32 in. | 36 | 41 | 46 | 51 | 7,360 lb |
| Grouted every 16 in. | 49 | 54 | 59 | 64 | 9,440 lb |
| Solid units, no grout | 56 | 68 | 80 | 92 | 12,800 lb |
| Hollow, grouted every cell | 74 | 79 | 84 | 89 | 13,440 lb |
| Wall | Blocks (5% waste) | Pallets |
|---|---|---|
| 10 × 8 ft | 95 | 2 |
| 20 × 8 ft | 189 | 3 |
| 30 × 8 ft | 284 | 4 |
| 40 × 8 ft | 378 | 5 |
| 1,000 ft² wall | 1,182 | 14 |
| Blocks | At $2.00 | At $3.00 | At $4.00 |
|---|---|---|---|
| 95 | $190 | $285 | $380 |
| 189 | $378 | $567 | $756 |
| 284 | $568 | $852 | $1,136 |
| 378 | $756 | $1,134 | $1,512 |
| 1,182 | $2,364 | $3,546 | $4,728 |
| Feature | Concrete block | Brick | Poured concrete |
|---|---|---|---|
| Face area per unit | About 0.89 ft² (8×16 face) | A small fraction of a ft² | Whole wall at once |
| Mortar per 80 lb bag | About 13 blocks | About 37 bricks | None |
| Needs formwork | No | No | Yes |
| Reinforcement | Rebar in grouted cores | Ties or reinforcement as designed | Rebar cage |
| Can be built in stages | Yes | Yes | Not mid-pour |
| Usual role | Structure, foundations, garden walls | Appearance or veneer | Slabs, footings, heavy walls |
| Measure | Imperial | Metric |
|---|---|---|
| Nominal block face | 8 × 16 in | about 203 × 406 mm |
| Actual block length | 15⅝ in | about 397 mm |
| Actual block height and width | 7⅝ in | about 194 mm |
| Blocks per area | 1.125 per ft² | about 12.1 per m² |
| Blocks per course | 0.75 per ft of wall | about 2.46 per m of wall |
| Courses per height | 1.5 per ft of wall | about 4.9 per m of wall |
Frequently Asked Questions About the CMU Block Calculator
How do I calculate how many concrete blocks I need?
Multiply the wall's length by its height to get the gross area, subtract any door or window openings, then multiply the result by 1.125 (the standard blocks-per-square-foot figure for an 8×16 inch block face). Add a waste allowance, typically 5%, and round up, since a partial block still means buying a whole one. Enter your own wall dimensions above for an exact figure rather than scaling a generic example.
How many sq ft is a CMU block?
A standard 8×8×16 inch CMU covers 0.889 square feet of wall face. Its actual size (7-5/8 × 7-5/8 × 15-5/8 inches) plus a standard 3/8 inch mortar joint brings it to a full nominal 8×16 inches, or 128 square inches. That's why the blocks-per-square-foot figure used throughout this calculator is 1.125 (1 divided by 0.889), regardless of how wide (thick) the block itself is.
How much is 1 CMU block?
Standard 8×8×16 inch concrete block typically runs somewhere around $1.50 to $3.50 each at retail, depending on region, supplier, and whether it's a basic gray block or a specialty type. Larger 10 or 12 inch block generally costs more per unit than 8 inch. Prices vary enough by local supplier that it's worth getting an actual quote rather than relying on a national average. Enter your own quoted price above for a real total.
How many bags of cement do I need for 100 blocks?
By default, this calculator uses about 3 to 4 bags of 70 lb masonry cement per 100 standard blocks, based on the Concrete Masonry & Hardscapes Association's estimate of roughly 30 blocks per bag. Masonry cement is mixed with sand on site. Pre-blended mortar mix, which has sand in the bag, lays fewer blocks per bag, commonly quoted at 9 to 15 blocks for a 60 to 80 lb bag. Change the coverage field above to match the product you are actually buying.
How much sand do I need for a block wall?
About 1 ton of masonry sand covers every 8 bags of masonry cement used, per CMHA's published material-estimating guidance, roughly 240 blocks' worth of mortar per ton of sand at standard coverage. This calculator computes sand directly from the mortar bag count above, so entering your wall's dimensions gives an exact figure rather than a rule-of-thumb estimate for your specific project.
What is the actual size of an 8x8x16 block?
An 8×8×16 inch CMU's real, as-manufactured size is 7-5/8 × 7-5/8 × 15-5/8 inches, per ASTM C90. The block is deliberately made 3/8 inch smaller than its nominal size in every direction so that a standard 3/8 inch mortar joint fills the gap and brings each course back out to a clean 8×16 inch module, which keeps courses aligned with other construction materials built on the same 4- or 8-inch grid.
What is 6 inch block used for?
6 inch concrete block is mainly used for non-load-bearing interior partition walls and lighter garden or landscape walls, where full structural width isn't needed. It's narrower than the standard 8 inch load-bearing block, which saves material and floor space but isn't rated for the same structural loads. Select 6 inch as the block width above if that's what your project calls for; the block-count math stays the same either way, since the face size doesn't change.
How do I calculate grout needed for block cores?
Turn on the solid-grout toggle above and this calculator estimates roughly a quarter cubic foot of grout per standard 8 inch block, scaled up for wider block since a wider block has a larger hollow core. Most walls aren't fully grouted; core-fill grout is mainly needed for reinforced walls with rebar running through the cores, foundation walls, and taller retaining walls that need the added strength a solid core provides.
Does this calculator work for cinder blocks too?
Yes. "Cinder block" is an older term for the same general product now made as a concrete masonry unit (CMU). Modern block uses concrete aggregate rather than the coal-cinder aggregate the original cinder blocks used, but the standard 8×16 inch face size and the blocks-per-square-foot math are identical. Enter your wall dimensions the same way regardless of which term your supplier uses.
What's the difference between cinder block and concrete block?
Historically, cinder block used coal cinders as its aggregate, while concrete block uses sand, gravel, or crushed stone. True cinder block is rarely manufactured today; most block sold under that name now is standard concrete block, and the two terms are largely used interchangeably in casual conversation. Structurally and dimensionally they're estimated the same way, which is why this one calculator covers both without needing a separate version.
How much does a concrete block wall cost?
Block material alone typically runs a few dollars per square foot of wall, driven mostly by block price and wall thickness. This calculator's cost output covers block material only. A fully installed wall, including mortar, labor, reinforcement, and any grout fill, commonly costs several times the raw block price per square foot once labor is included, and varies widely by region and wall complexity, so a local contractor quote is the only way to get an installed total.
How many blocks for a 100 sq ft wall?
At the standard 1.125 blocks per square foot plus a 5% waste allowance, a 100 square foot wall needs about 119 standard 8×8×16 inch blocks. That figure assumes no door or window openings cut into that 100 square feet; subtract any opening area first if the wall has one, since blocks aren't laid where an opening sits.
Do I need to subtract door and window openings?
Yes. Blocks aren't laid across a door or window opening, so subtracting that area before calculating block count avoids over-ordering. Enter the combined square footage of all openings in the wall in the "doors, windows & openings" field above; the calculator subtracts that from the gross wall area before applying the blocks-per-square-foot figure, giving a net block count that matches what actually gets built.
How much extra block should I order for waste?
5% is a reasonable default waste allowance for a straightforward rectangular wall with standard cuts, and it's already baked into this calculator's default. A wall with more corners, angled cuts, or a less experienced crew can run higher, sometimes 8-10%, while a simple straight run with few cuts can sometimes get by with less. Adjust the waste percentage field above to match your specific project's complexity.
What mortar type should I use, Type N or Type S?
Type N mortar is the general-purpose choice for most above-grade, non-structural block walls, including garden walls and interior partitions. Type S, a higher-strength mix, is typically specified for load-bearing walls, foundation walls, and anything below grade or exposed to significant lateral load, since it bonds more strongly and resists moisture better. Local building code and a structural engineer's specification, where one applies, should always take priority over a general rule of thumb.
How many concrete blocks does an average house need?
There's no single answer. It depends entirely on the house's foundation type, wall height, and whether block is used just for the foundation or for full exterior walls. A typical block foundation wall for a mid-size house might use anywhere from several hundred to over a thousand blocks; the only reliable way to get a real number is to measure the actual wall lengths and heights involved and run them through the calculator above.
How many blocks do I need for a 10x10 shed?
It depends on the foundation height. A 10 by 10 shed has a 40 foot perimeter. At 2 feet high (3 courses) that is 80 square feet, or 95 blocks with 5% waste. At 4 feet high (6 courses) it is 160 square feet, or 189 blocks. Enter 40 as the length and your wall height above, and subtract any door gap.
How many blocks do I need for a 10x12 shed?
A 10 by 12 shed has a 44 foot perimeter. At 2 feet high that is 88 square feet and 104 blocks with 5% waste. At 4 feet high it is 176 square feet and 208 blocks. The calculator uses 1.125 blocks per square foot, so enter 44 as the wall length and your own height to adjust the total.
How many blocks do I need for a 4x4 room?
A 4 by 4 foot enclosure has a 16 foot perimeter. At 8 feet high that is 128 square feet, or 152 blocks with 5% waste. Subtracting a 3 by 7 foot door (21 square feet) leaves 107 square feet and 127 blocks. If you mean 4 by 4 metres, the perimeter is about 52.5 feet, so enter that length instead.
How many blocks do I need for 1,000 square feet?
A 1,000 square foot wall needs 1,125 blocks before waste, since each square foot takes 1.125 standard 8×16 inch blocks. With a 5% waste allowance the order is 1,182 blocks. Subtract any door and window area first, because openings can remove a noticeable share of a large wall, and change the waste percentage if your site calls for more.
How many bags of mortar do I need for 1,000 blocks?
It depends on the bag. At CMHA's rate of about 30 blocks per 70 lb bag of masonry cement, 1,000 blocks takes 34 bags. A sanded 80 lb pre-blended mix that lays about 13 blocks per bag takes 77 bags. Check the coverage printed on your bag and enter it in the blocks-per-bag field for an exact count.
How many blocks come on a pallet?
A pallet of standard 8×8×16 block is commonly listed at 90 blocks, but the count varies by block size and type, and yards quote anything from the low 70s to over 100. Ask your supplier for the exact count before ordering. Divide the calculator's block total by that number and round up to get the number of pallets.
How much does a concrete block weigh?
Weight depends on the concrete density. CMHA lists hollow, ungrouted 8 inch walls at 24 to 39 pounds per square foot for 85 to 145 pcf units. With 1.125 blocks per square foot, that works out to roughly 21 to 35 pounds each, including a share of mortar. Grouted cores add substantially more.
What is the mortar ratio for concrete block?
By volume, portland cement to lime to damp loose sand is 1 : ½ : 4½ for Type S and 1 : 1 : 6 for Type N, with Type M at 1 : ¼ : 3¾. Sand must be 2¼ to 3 times the cement and lime combined. A pre-blended bag already contains sand, so follow its label.
How many blocks does an 80 lb bag of mortar lay?
QUIKRETE's data sheet for its 80 lb Mason Mix says one bag will lay up to 13 standard 8×8×16 blocks, or up to 37 standard bricks. That is a pre-blended mix with the sand already in the bag. Masonry cement sold without sand goes further, which is why CMHA's figure is about 30 blocks per 70 lb bag.
How much does a 12x8x16 block cost?
Price depends on your region, the supplier, and whether you buy by the piece or the pallet, so there is no single reliable figure. A 12 inch block costs more than an 8 inch block because it uses more material. Get a quote from a local yard, then enter it in the price field to see the wall total.
Is a block wall cheaper than a poured concrete wall?
It depends on the size and the labor. Block avoids formwork and can be built in stages, which suits small walls and owner builders. Poured concrete avoids mortar joints and goes up in one pour, which suits long or tall walls. Price both for your own wall, including rebar, grout, forms and labor.
How much grout fills the cores of an 8x8x16 block?
This calculator uses about 0.25 cubic feet of grout per standard 8 inch block, scaled by block width, which is an engineering approximation and not a fixed trade figure. At that rate, 100 blocks take about 0.93 cubic yards. Actual core volume varies by manufacturer, so confirm it with your supplier before ordering grout.
What are the actual dimensions of a CMU block in mm?
A nominal 8×8×16 block is about 203 × 203 × 406 mm. CMHA's unit drawing gives the actual size as 15.625 inches long (397 mm) and 7.625 inches wide and high (194 mm). The 3/8 inch mortar joint brings the finished course to the nominal 8×16 inch module.
How many courses of block are in an 8-foot wall?
An 8 foot wall is 12 courses of standard block, since each course measures 8 inches including its mortar joint. Heights that are not a multiple of 8 inches, such as 3 feet, end in a part course that has to be cut or planned around. The coursing chart on this page lists whole-course heights.
What is a bond beam block?
CMHA defines a bond beam block as a hollow unit with depressed or knock-out webs, so horizontal reinforcing steel and grout can be placed through it. Bond beams are grouted, reinforced courses that tie a wall together. Count them separately from standard blocks if your design calls for them.
References
- [1] Concrete Masonry & Hardscapes Association. “TEK 04-02A: Estimating Concrete Masonry Materials.” CMHA. Accessed 2026-09-28.
- [2] ASTM International. “C90 Standard Specification for Loadbearing Concrete Masonry Units.” ASTM. Accessed 2026-09-28.
- [3] Concrete Masonry & Hardscapes Association. “TEK 09-01A: Mortar for Masonry.” CMHA. Accessed 2026-10-04.
- [4] Concrete Masonry & Hardscapes Association. “TEK 01-04: Glossary of Concrete Masonry Terms.” CMHA. Accessed 2026-10-04.
- [5] Concrete Masonry & Hardscapes Association. “CMU-TEC-002-23: Wall Weights.” CMHA. Accessed 2026-10-04.
- [6] QUIKRETE. “Mason Mix No. 1136 data sheet.” QUIKRETE. Accessed 2026-10-04.
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