Concrete Yard Calculator

Concrete is sold by the cubic yard, or by the cubic metre outside the US, so every pour has to become a volume first. The calculator finds the volume of the shape you choose, adds a waste percentage, and shows the result in cubic yards, cubic feet and cubic metres. It also converts the order into bags of 40, 60 and 80 pounds and gives the weight.

The formula for concrete yardage is the same for every shape: find the volume in cubic feet, then divide by 27. A cubic yard is a cube 3 feet on each side, and 3 × 3 × 3 is 27 cubic feet, as Wikipedia's entry on the cubic yard defines it. Using a slab as the example, the volume in cubic feet is length x width x thickness in feet, and since thickness is measured in inches you divide it by 12.

To calculate concrete yards by hand, write down each dimension, convert the thickness to feet, multiply, divide by 27 and add your waste. The calculator does the same steps instantly and handles the less common shapes.

A slab is the simplest pour. A 10 × 10 ft slab 4 inches thick holds 33.3 cubic feet, 1.23 cubic yards. A 40 × 60 ft slab 4 inches thick holds 29.63 yards. The slab table lists sizes from 10 × 10 up to 40 × 60 at 4, 5 and 6 inches, and the per 100 square feet table gives the quick rule: 100 square feet at 4 inches is 1.23 cubic yards.

One cubic yard covers 81 square feet at 4 inches, 64.8 at 5 inches and 54 at 6 inches. County Materials, a concrete producer, recommends a minimum of 4 inches for a driveway and says thickness matters more than the strength of the concrete for load capacity.

If your slab has a thicker edge, price the edge as a footing and add it. If the pour is an odd shape, split it into rectangles and triangles and add the volumes.

A footing is a long, narrow pour. Enter the length in feet and the width and depth in inches. A footing 80 feet long, 16 inches wide and 8 inches deep holds 71.1 cubic feet, 2.63 yards. The footing table gives the yards per 100 linear feet for common widths and depths.

For posts, piers and sonotube columns, choose column or round hole. The calculator uses 3.14159 times the radius squared times the height, times the number of holes. Twelve inches wide and 3 feet deep is 2.36 cubic feet per hole, which is 6 bags of 60 lb mix.

A post sits inside the hole and takes up space. The calculator counts the full hole, so the real need is slightly less. Keep the difference as your waste.

A wall is length x height x thickness. A wall 20 ft long, 4 ft high and 8 inches thick holds 53.3 cubic feet. Choose wall for solid poured walls only. Block walls use a different calculation.

Stairs are treated as solid steps. Each step is a block as wide as the stair, as deep as the run and as tall as the rise above the ground, and the blocks stack, so a flight of n steps holds width x run x rise x n x (n + 1) / 2. Four steps 4 feet wide with a 10 inch run and 7 inch rise hold 19.4 cubic feet. If the stairs are hollow or sit on a slab, the real figure is lower or higher.

A triangle slab, such as a corner pad, is half the base times the height times the thickness. A base of 12 feet and a height of 9 feet at 4 inches holds 18.0 cubic feet.

For small jobs you buy bags. The yield is the volume of finished concrete one bag makes. For QUIKRETE Concrete Mix No. 1101, the data sheet lists 0.3 cubic feet for a 40 lb bag, 0.375 for 50 lb, 0.45 for a 60 lb bag and 0.60 for an 80 lb bag. The calculator uses those figures as its default. Other brands and mixes differ, so read your bag and enter the yield in the own yield box if it is not the same.

One cubic yard is 45 bags of 80 lb mix, 60 of 60 lb or 90 of 40 lb. The calculator rounds up to whole bags, using the order volume including waste. For anything over a cubic yard, a ready-mix delivery is usually easier, but compare prices, and ask about minimum load charges, which the National Ready Mixed Concrete Association lists as an item to agree when ordering.

The QUIKRETE data sheet gives a unit weight of about 140 pounds per cubic foot, which is 3,780 pounds per cubic yard, 1.89 tons. The calculator uses 140 as its default and lets you change it. Three cubic yards weigh about 5.67 tons. Check the weight against the capacity of your truck, trailer or floor.

Ratios such as 1:2:4 and 1:2:3 describe a batch by volume, in parts of cement, sand and coarse stone. A 1:2:4 mix has 7 parts, so cement is one seventh of the dry mix. The ratio table shows the shares. The dry materials take up more room than the finished concrete, so the calculator's volume is the finished concrete, and a mix designer or supplier converts it to dry quantities.

For metric work, choose metric and enter metres and centimetres. One cubic metre is 1.308 cubic yards or 35.31 cubic feet.

Order 5 to 10 percent more than the calculated volume. The ground is rarely perfectly flat, forms flex, and some concrete is lost in handling. Running short in the middle of a pour is far worse than having a little left over. The calculator starts at 10 percent, and you can change it.

A typical slab goes in this order. Prepare a firm, uniform subgrade and base, damp but not muddy. Set forms to the thickness you want, with the slope for drainage, which County Materials gives as at least 1/4 inch per foot for a driveway. Place any reinforcement, which that producer notes is optional but often used and should sit in the upper third of the slab. Pour, screed, float, finish, cut or tool joints, and cure.

This page estimates quantity. It does not design a slab. Structural slabs, footings and walls need a design that follows local code, and a qualified professional should check them.

The estimate assumes the dimensions you enter are exact, the thickness is uniform and the shape is solid. It does not include rebar, voids, a thickened edge, spillage or the concrete left in the truck. Bag yields come from one manufacturer's data sheet and other products differ. Treat every result as an estimate, follow the bag label or your supplier, and have a professional check structural work.

For the base under a slab, use the gravel calculator. For steps, see the stair calculator, and for block walls try the CMU block calculator.