Pool Water Volume Calculator
Pool water volume calculator for rectangular, round, oval and irregular pools. Get gallons, litres, fill time and fill cost from size and depth.
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How the Pool Water Volume Calculator Formula Works
A pool is a prism with a sloping floor, so its volume is the area of the water surface times the average depth. The average depth is the shallow end depth plus the deep end depth, divided by two, which works for a floor that slopes steadily.
The area depends on the shape. A rectangle is length times width. A round pool is pi over four times the diameter squared. An oval is pi over four times the long diameter times the short diameter, and a free-form pool uses its surface area directly. Multiply the area by the average depth to get cubic feet.
One cubic foot holds 7.48 US gallons, so multiply by 7.48 for gallons. The shortcut multipliers you see, 7.5 for a rectangle and 5.9 for a round or oval pool, are those same numbers rounded, because pi over four times 7.48 is 5.875. In metric, area in square metres times average depth in metres is cubic metres, and each cubic metre is 1,000 litres. Add a flow rate and a price and the calculator also estimates the fill time and cost.
gallons = surface area (sq ft) × average depth (ft) × 7.48; average depth = (shallow end + deep end) / 2; round or oval area = pi/4 × diameters- length, width, diameterft or mWater surface dimensions for the chosen shape.
- shallow end depthft or mDepth of the water at the shallow end.
- deep end depthft or mDepth of the water at the deep end.
- fill rategpm or L/minOptional flow rate to estimate the fill time.
- water price$ per 1,000 gal or per m3Optional, to estimate the cost of the water.
- length, width, diameter
- ft or m
- Water surface dimensions for the chosen shape.
- shallow end depth
- ft or m
- Depth of the water at the shallow end.
- deep end depth
- ft or m
- Depth of the water at the deep end.
- fill rate
- gpm or L/min
- Optional flow rate to estimate the fill time.
- water price
- $ per 1,000 gal or per m3
- Optional, to estimate the cost of the water.
Using the Pool Water Volume Calculator
Enter units
Choose from Feet and US gallons, Metres and litres.
Enter pool shape
Choose from Rectangle, Round, Oval, Known surface area (free-form).
Enter length (feet or metres)
Type the figure you already have, then press Calculate.
Enter width (feet or metres)
Type the figure you already have, then press Calculate.
Enter diameter (feet or metres)
Type the figure you already have, then press Calculate.
Enter long diameter (feet or metres)
Type the figure you already have, then press Calculate.
Enter short diameter (feet or metres)
Type the figure you already have, then press Calculate.
Enter surface area (sq ft or sq m)
Type the figure you already have, then press Calculate.
Enter shallow end depth (feet or metres)
Type the figure you already have, then press Calculate.
Enter deep end depth (feet or metres)
Type the figure you already have, then press Calculate.
Enter fill rate (gallons or litres per minute, optional)
Type the figure you already have, then press Calculate. This one is optional.
Enter water price ($ per 1,000 gallons or per m3, optional)
Type the figure you already have, then press Calculate. This one is optional.
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 rectangular pool is 32 feet long and 16 feet wide, 3 feet deep at the shallow end and 6 feet at the deep end. The surface area is 512 square feet and the average depth is (3 + 6) / 2 = 4.5 feet.
The volume is 512 × 4.5 = 2,304 cubic feet, which is 2,304 × 7.4805 = 17,235 US gallons, or 65,242 litres. At 10 gallons a minute it takes 28.7 hours to fill, and at $5 per 1,000 gallons the water costs about 86.18 dollars.
A 40 x 20 ft pool, 3 to 8 ft deep
A 40 by 20 foot pool is 800 square feet. With depths of 3 and 8 feet the average is 5.5 feet, so the volume is 4,400 cubic feet.
That is 32,914 US gallons, or 124,594 litres. Filling at 10 gallons a minute takes 54.9 hours, about 2.3 days.
A round pool, 18 ft across and 4 ft deep
Choose round, enter a diameter of 18 feet and set both depths to 4 feet. The area is pi / 4 × 18 squared = 254.5 square feet.
The volume is 1,017.9 cubic feet, which is 7,614 US gallons or 28,823 litres. The shortcut 18 × 18 × 4 × 5.9 gives 7,646, within half a percent.
An oval pool, 25 x 12 ft, 3.5 to 5.5 ft deep
An oval pool 25 feet long and 12 feet wide has an area of pi / 4 × 25 × 12 = 235.6 square feet. The average depth is (3.5 + 5.5) / 2 = 4.5 feet.
The volume is 1,060.3 cubic feet, which is 7,931 US gallons or 30,024 litres. At 8 gallons a minute the fill takes 16.5 hours.
A free-form pool with 600 sq ft of surface
Choose known surface area, and enter 600 square feet. With depths of 4 and 6 feet the average is 5 feet, so the volume is 3,000 cubic feet.
That is 22,442 US gallons, or 84,951 litres. Filling at 10 gallons a minute takes 37.4 hours.
Metric: 10 m x 4 m, 1 to 2 m deep
Choose metric and enter 10 metres by 4 metres with depths of 1 and 2 metres. The area is 40 square metres and the average depth is 1.5 metres.
The volume is 60 cubic metres, which is 60,000 litres or 15,850 US gallons. At 40 litres a minute it takes 25 hours to fill, and at 2 dollars per cubic metre the water costs 120 dollars.
What Else to Know
How Pool Volume Is Calculated
The volume of a pool is the area of the water surface multiplied by the average depth. Pool Breeze gives the same method: length x width x average depth for a rectangle, and surface area x average depth for a free-form pool.
The calculator finds the area for the shape you choose, averages the two depths you enter, and multiplies. The result is shown in US gallons, litres, cubic feet and cubic metres at the same time.
Optional boxes for the fill rate and the water price add an estimate of the time and cost to fill the pool.
Average Depth
Most pools slope from a shallow end to a deep end. Add the two depths and divide by two to get the average depth, as Pool Breeze describes. A pool 3 feet at one end and 6 feet at the other averages 4.5 feet.
The average works when the floor slopes steadily. A pool with a deep hopper or a sudden drop will not match it exactly, so for those shapes check the volume the pool maker states.
Use the depth of the water, not the structural depth, since pools are usually kept below the top.
Shapes and Multipliers
A rectangle is length times width. A round pool is pi over four times the diameter squared. An oval is pi over four times the long diameter times the short one. A free-form pool uses its surface area, which you can find by splitting it into simple shapes.
One cubic foot holds 7.48 US gallons, from the definition of a US gallon as 231 cubic inches. That gives the familiar 7.5 for a rectangle. For round and oval pools pi / 4 × 7.48 is 5.875, rounded to 5.9. The multiplier table shows the numbers.
The calculator uses the unrounded values, so its answers differ slightly from the rules of thumb.
Common Pool Sizes
The tables list rectangular, round and oval pools of common sizes at several depths. A 16 × 32 ft pool at an average of 4.5 ft holds about 17,235 gallons, and an 18 ft round pool 4 ft deep holds about 7,614.
There is no standard size, so the tables are examples. Your own measurements, with the real shallow and deep end depths, will give a better figure than a table.
If you know the volume the pool maker or builder stated, use that and compare it with the calculator.
Fill Time and Cost
To estimate the time to fill, divide the gallons by the flow rate and by 60. At 10 gallons a minute, 5,000 gallons takes 8.3 hours and 17,235 gallons takes 28.7 hours. Measure the real flow from your hose or supply for a better figure.
The cost is the gallons divided by 1,000 and multiplied by your price per 1,000 gallons. The calculator does not know your water rates, so it uses the price you enter. Bulk water delivery has its own pricing, so compare a delivery quote for the same volume.
Water price tables in the guide use placeholder prices, not real rates.
Chemicals, Heaters and Salt
Pool volume is the starting point for chemical doses, but this calculator does not recommend any. Follow the instructions on your product label, which state the amount for a given volume, and the manual for your equipment.
Heater size depends on the temperature rise, the climate and covers as well as volume, so ask a heater maker or pool professional.
For salt, use the pool salt calculator with the gallons you find here.
Accuracy and Limits
The estimate is as good as your measurements. Measure the water surface, not the outside of the coping, and measure the depths at the shallow and deep ends. A steady slope is assumed.
The calculator does not model steps, benches, a deep hopper or a curved floor, and it does not subtract the water displaced by swimmers. For a pool with these features, the maker's stated volume is the better figure.
For a spa or hot tub the same approach works for simple shapes, using the depth of the water.
Reference Tables
| Term | Meaning |
|---|---|
| Pool volume | The amount of water the pool holds, in gallons or litres |
| Average depth | (shallow end + deep end) / 2 for a pool with a sloping floor |
| Surface area | The area of the water surface, used for free-form pools |
| Water level | The pool is usually kept below the top; the calculator uses the depth you enter |
| Turnover | The time to circulate the whole volume through the filter |
| US gallon | 231 cubic inches, 3.785411784 litres |
| Shape | Volume in cubic feet | Gallons | Rule of thumb multiplier |
|---|---|---|---|
| Rectangle | length x width x avg depth | x 7.48 | 7.5 |
| Round | pi/4 x diameter2 x avg depth | x 5.875 | 5.9 |
| Oval | pi/4 x long x short x avg depth | x 5.875 | 5.9 |
| Known surface area | area x avg depth | x 7.48 | 7.5 |
| Shallow end (ft) | Deep end (ft) | Average depth (ft) |
|---|---|---|
| 3 | 5 | 4 |
| 3 | 6 | 4.5 |
| 3.5 | 5.5 | 4.5 |
| 3 | 8 | 5.5 |
| 4 | 8 | 6 |
| 4 | 4 | 4 |
| 3 | 10 | 6.5 |
| 5 | 9 | 7 |
| Pool size (ft) | Area (sq ft) | Avg 4 ft | Avg 5 ft | Avg 6 ft |
|---|---|---|---|---|
| 12 × 24 | 288 | 8,618 | 10,772 | 12,926 |
| 14 × 28 | 392 | 11,729 | 14,662 | 17,594 |
| 15 × 30 | 450 | 13,465 | 16,831 | 20,197 |
| 16 × 32 | 512 | 15,320 | 19,150 | 22,980 |
| 18 × 36 | 648 | 19,390 | 24,237 | 29,084 |
| 20 × 40 | 800 | 23,938 | 29,922 | 35,906 |
| 20 × 44 | 880 | 26,331 | 32,914 | 39,497 |
| 25 × 50 | 1,250 | 37,403 | 46,753 | 56,104 |
| 30 × 60 | 1,800 | 53,860 | 67,325 | 80,790 |
| Diameter (ft) | Area (sq ft) | 3 ft deep | 4 ft deep | 5 ft deep |
|---|---|---|---|---|
| 12 | 113.1 | 2,538 | 3,384 | 4,230 |
| 15 | 176.7 | 3,966 | 5,288 | 6,610 |
| 18 | 254.5 | 5,711 | 7,614 | 9,518 |
| 21 | 346.4 | 7,773 | 10,364 | 12,955 |
| 24 | 452.4 | 10,152 | 13,536 | 16,921 |
| 27 | 572.6 | 12,849 | 17,132 | 21,415 |
| 30 | 706.9 | 15,863 | 21,151 | 26,438 |
| 33 | 855.3 | 19,194 | 25,592 | 31,990 |
| Size (ft) | Area (sq ft) | Avg 4 ft | Avg 5 ft | Avg 6 ft |
|---|---|---|---|---|
| 12 × 24 | 226.2 | 6,768 | 8,460 | 10,152 |
| 15 × 30 | 353.4 | 10,575 | 13,219 | 15,863 |
| 16 × 32 | 402.1 | 12,032 | 15,040 | 18,049 |
| 18 × 33 | 466.5 | 13,959 | 17,449 | 20,939 |
| 20 × 40 | 628.3 | 18,801 | 23,501 | 28,201 |
| 21 × 41 | 676.2 | 20,234 | 25,293 | 30,351 |
| Size (m) | Avg 1.2 m | Avg 1.5 m | Avg 2 m | Litres at 1.5 m |
|---|---|---|---|---|
| 6 × 3 | 21.6 | 27.0 | 36.0 | 27,000 |
| 8 × 4 | 38.4 | 48.0 | 64.0 | 48,000 |
| 10 × 4 | 48.0 | 60.0 | 80.0 | 60,000 |
| 12 × 5 | 72.0 | 90.0 | 120.0 | 90,000 |
| 15 × 6 | 108.0 | 135.0 | 180.0 | 135,000 |
| Pool volume (gal) | 5 gpm | 10 gpm | 15 gpm | 20 gpm |
|---|---|---|---|---|
| 5,000 | 16.7 h | 8.3 h | 5.6 h | 4.2 h |
| 10,000 | 33.3 h | 16.7 h | 11.1 h | 8.3 h |
| 15,000 | 50.0 h | 25.0 h | 16.7 h | 12.5 h |
| 20,000 | 66.7 h | 33.3 h | 22.2 h | 16.7 h |
| 25,000 | 83.3 h | 41.7 h | 27.8 h | 20.8 h |
| 30,000 | 100.0 h | 50.0 h | 33.3 h | 25.0 h |
| Pool volume (gal) | $2 per 1,000 | $5 per 1,000 | $8 per 1,000 | $12 per 1,000 |
|---|---|---|---|---|
| 5,000 | $10.00 | $25.00 | $40.00 | $60.00 |
| 10,000 | $20.00 | $50.00 | $80.00 | $120.00 |
| 15,000 | $30.00 | $75.00 | $120.00 | $180.00 |
| 20,000 | $40.00 | $100.00 | $160.00 | $240.00 |
| 25,000 | $50.00 | $125.00 | $200.00 | $300.00 |
| 30,000 | $60.00 | $150.00 | $240.00 | $360.00 |
| Mistake | Effect | Fix |
|---|---|---|
| Using the deepest depth instead of the average | Overstates volume | Average the shallow and deep ends |
| Measuring the outside of the coping | Overstates volume | Measure the water surface |
| Using 7.5 for a round pool | About 28 percent too high | Use 5.9 or the calculator |
| Mixing metres and feet | Large error | Set the unit first |
| Ignoring a sloped floor with a hopper | A few percent error | Use the maker's stated volume |
Frequently Asked Questions About the Pool Water Volume Calculator
How do I calculate the water volume of a pool?
Find the surface area, multiply by the average depth for cubic feet, then by 7.48 for US gallons. A 16 × 32 ft pool with an average depth of 4.5 ft is 2,304 cubic feet, which is 17,235 gallons. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
What is the pool volume formula?
For a rectangle, gallons = length x width x average depth x 7.48. For a round or oval pool use 5.9 in place of 7.48, because pi / 4 × 7.48 is about 5.875. For a free-form pool, use the surface area x average depth x 7.48. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
What is the volume of a 16x32 pool?
At an average depth of 4 feet it holds 15,320 gallons, at 5 feet 19,150 and at 4.5 feet 17,235. A 16 × 32 ft pool is 512 square feet, so the depth decides the volume. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
How many gallons is a 40x20 pool?
A 40 × 20 ft pool is 800 square feet. With an average depth of 4 feet it is 23,938 gallons, with 5 feet 29,922 and with 5.5 feet 32,914. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
How do I find the average depth?
Add the shallow end depth and the deep end depth and divide by two. A pool that is 3 feet at one end and 8 feet at the other averages 5.5 feet. This works for a floor that slopes steadily, and the average depth table lists common pairs. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
How do I calculate the volume of a round pool?
Square the diameter, multiply by pi / 4 for the area, then by the depth and 7.48. An 18 ft round pool 4 ft deep is 254.5 sq ft and 7,614 gallons. The shortcut diameter x diameter x depth x 5.9 gives nearly the same. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
How do I calculate the volume of an oval pool?
Multiply the long diameter by the short diameter, by pi / 4, by the average depth and by 7.48. A 25 × 12 ft oval at 4.5 ft average depth is 7,932 gallons. The rule of thumb is long x short x depth x 5.9. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
How do I calculate the volume of an irregular or kidney-shaped pool?
Estimate the surface area, then multiply by the average depth and 7.48. Pool Breeze describes a free-form pool as surface area x average depth. Break the shape into rectangles, circles and triangles to find the area, then use the known area option. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
How many litres are in a pool?
Multiply the volume in cubic metres by 1,000. A pool 10 m long, 4 m wide and 1.5 m deep on average is 60 cubic metres, which is 60,000 litres, or 15,850 US gallons. Choose metric in the calculator. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
How much does it cost to fill a 10,000 gallon pool?
Multiply the gallons by your price per gallon. At $5 per 1,000 gallons, 10,000 gallons costs $50.00, and at $8 it costs $80.00. Prices vary by utility and by delivery, so enter your own rate from your water bill. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
How long will it take to fill a 5,000 gallon pool?
Divide the gallons by the flow rate per minute and by 60 for hours. At 10 gallons per minute it takes 8.3 hours, and at 5 gallons per minute 16.7 hours. Measure your own hose flow for a better estimate. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
Is it cheaper to fill a pool by hose or truck?
It depends on local water prices, delivery fees and the size of the pool, none of which the calculator knows. Enter your price per 1,000 gallons for the hose figure and compare it with a delivery quote for the same gallons. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
What does a 25,000 gallon pool look like?
It depends on the shape and depth. A 20 × 40 ft pool needs an average depth of 4.2 ft to hold 25,000 gallons, and an oval of 21 × 41 ft needs 4.9 ft. Try dimensions in the calculator. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
Is 16,000 gallons a big pool?
It is a medium pool. A 16 × 32 ft rectangle at an average of 4.5 ft holds about 17,235 gallons, and an 18 ft round pool at 4 ft holds 7,614. Whether it is big depends on what you compare it with. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
How many gallons are in a round pool?
At a 4 foot depth, a 15 ft round pool holds 5,288 gallons, an 18 ft pool 7,614 and a 24 ft pool 13,536. The round pool table lists other diameters and depths. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
How many chlorine tablets do I need for my pool volume?
This calculator does not give chemical doses. Use the volume it gives with the instructions on your product label, which state how much to add for each 10,000 gallons or similar. Dosing depends on the product and the water, so follow the label. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
How big a pool heater do I need?
This calculator does not size heaters. It gives the volume, which is one input that heater makers use. Heater size also depends on the temperature rise, the climate, covers and wind, so ask the heater maker or a pool professional. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
How do I calculate how much salt my pool needs?
Work out the volume here, then use the pool salt calculator on this site with the gallons. It uses the volume and your target level to find the salt to add. Check your chlorine generator's manual for its target. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
Should I use the water level or the full depth?
Use the depth of the water. Pools are usually kept a few inches below the top, so the full structural depth overstates the volume slightly. Measure from the pool floor to the normal water line when you can. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
Why do calculators use 7.5 or 5.9?
They are rounded multipliers. One cubic foot holds 7.48 US gallons, so 7.5 works for a rectangle. For round and oval pools multiply by pi / 4, giving 5.875, rounded to 5.9. The calculator uses the unrounded values. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
How accurate is the pool volume estimate?
It is as good as your measurements. The average depth method assumes a steady slope, so a pool with a deep hopper or a sudden drop holds more or less than the estimate. Check the figure against the pool maker's stated volume when you can. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
Can I use this for a spa or hot tub?
Yes, if it is a rectangle, circle, oval or a known surface area. Enter the dimensions and the depth of the water. For a small spa, the water displaced by people changes the volume slightly, which the calculator does not include. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
How do I use this pool water volume calculator?
Choose feet or metres, pick the shape, enter the dimensions and the shallow and deep end depths. Add a fill rate and a water price if you want the fill time and cost. The results show gallons, litres, cubic feet, cubic metres and the fill estimate. Enter your own dimensions and depths in the calculator for an exact figure in gallons, litres and cubic metres.
References
- [1] Pool Breeze. “Calculate pool volume.” Pool Breeze. Accessed 2026-10-06.
- [2] Clorox Pool. “Pool volume calculator.” Clorox Pool. Accessed 2026-10-06.
- [3] Wikipedia contributors. “Gallon.” Wikipedia. Accessed 2026-10-06.
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