Pool Volume Calculator
Calculate how many gallons of water your swimming pool holds. Works for rectangular, round and oval pools with a shallow end and a deep end.
By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Pool volume
- 15,989 gal
- At 7.48 gallons per cubic foot
- Volume of water
- 2,138 cu ft
- 79.2 cu yd
- Surface area
- 450 sq ft
- Average depth
- 4.75 ft
- (Shallow end + deep end) / 2
- Weight of water
- 66.7 tons
- At 8.34 lb per gallon
Pool Volume formula
Average depth = (Shallow depth + Deep depth) / 2
Rectangle area = Length x Width; Round area = 3.1416 x (Diameter / 2)²; Oval area = 3.1416 x (Length / 2) x (Width / 2)
Cubic feet = Area x Average depth
Gallons = Cubic feet x 7.48Worked example
A 16 x 32 ft rectangular in-ground pool, 3 ft in the shallow end and 8 ft at the deep end: average depth = (3 + 8) / 2 = 5.5 ft. 16 x 32 = 512 sq ft, and 512 x 5.5 = 2,816 cubic feet. 2,816 x 7.48 = 21,064 gallons.
A 24 ft round above-ground pool filled to 4 ft: area = 3.1416 x 12² = 452.4 sq ft. 452.4 x 4 = 1,809.6 cubic feet, and 1,809.6 x 7.48 = about 13,536 gallons.
Quick reference
| Pool | Average depth | Surface area | Gallons |
|---|---|---|---|
| 12 x 24 ft rectangle | 5 ft | 288 sq ft | 10,771 |
| 15 x 30 ft rectangle | 5 ft | 450 sq ft | 16,830 |
| 16 x 32 ft rectangle | 5 ft | 512 sq ft | 19,149 |
| 18 x 36 ft rectangle | 5 ft | 648 sq ft | 24,235 |
| 20 x 40 ft rectangle | 5 ft | 800 sq ft | 29,920 |
| 24 ft round | 4 ft | 452 sq ft | 13,535 |
| 27 ft round | 4 ft | 573 sq ft | 17,131 |
| 15 x 30 ft oval | 4 ft | 353 sq ft | 10,575 |
How to calculate pool volume
Measure the pool's length and width (or diameter) in feet and multiply for the surface area. Round pools use pi times the radius squared, and ovals use pi times half the length times half the width. Multiply the area by the average depth for cubic feet, then by 7.48 for gallons.
For a sloped bottom, averaging the two depths is close enough for dosing; a flat shallow end with a small hopper holds 5 to 10 percent less. Treat a kidney pool as an oval or two overlapping rectangles. Measure water depth, not wall height: a 52 inch above-ground wall runs about 48 inches of water. A replacement liner is not sized from gallons; the maker's sheet wants wall lengths, corner radius, depths at the break and hopper, and A-B triangulation.
Why the number matters
Every chemical dose is per 10,000 gallons, so a 20 percent volume error is a 20 percent error in every dose. Per 10,000 gallons, 1 lb of 65 percent cal-hypo raises free chlorine about 7 ppm and 1 gallon of 12.5 percent liquid chlorine about 12 ppm. Stabilizer at 13 oz per 10,000 gallons raises CYA 10 ppm. A salt system needs about 27 lb of salt per 1,000 gallons to reach 3,200 ppm. Test first, then dose to the label.
Volume also sizes the equipment. The pump should turn the pool over in 8 to 10 hours, about 40 gpm for 20,000 gallons; since the 2021 DOE standard, new pumps over about 1 hp are variable speed, so run low speed for 24 hours instead. A 400,000 BTU gas heater raises 20,000 gallons about 2°F an hour.
What this calculator leaves out
The result is water volume only. Not included: the actual liner size, salt, stabilizer and filter sizing. Fill cost is typically $5 to $10 per 1,000 gallons of municipal water in 2026, or $300 to $600 for a 6,000 gallon tanker; a garden hose takes about 33 hours per 20,000 gallons.
Mistakes that cost money
- Measuring wall height instead of water depth: a 52 in above-ground wall holds about 48 in of water, an 8 percent error in every dose.
- Muriatic acid dosed on an inflated gallon figure drops pH under 7.0, etches plaster and pits the heater core; dose half, retest in 4 hours.
- Ordering a liner by nominal size (16 x 32) instead of the maker's A-B measurement sheet gets a liner that wrinkles or misses the track.
- Cal-hypo shock poured into a skimmer that feeds a trichlor tab feeder can explode; broadcast shock across the deep end with the pump running.
- A pump bigger than the filter's flow rating (sand filters 20 gpm per sq ft) channels the sand and passes dirt; size the filter first.
- Filling from the tap bills sewer charges on 20,000 gallons; many utilities credit a pool fill if you call before, not after.
Key facts
- One cubic foot of water is 7.48 US gallons and weighs 62.4 lb; one gallon weighs 8.34 lb.
- A 16 x 32 ft in-ground pool with an average depth of 5 ft holds about 19,000 gallons.
- One pound of 65% calcium hypochlorite raises free chlorine by about 7 ppm in 10,000 gallons of water.
- A pool pump should turn over the full volume of the pool in 8 to 10 hours; a 20,000 gallon pool needs about 40 gallons per minute.
- Filling a 20,000 gallon pool from a garden hose at 10 gallons per minute takes about 33 hours.
Frequently asked questions
How many gallons is a 16 x 32 pool?
With an average depth of 5 ft, 16 x 32 x 5 = 2,560 cubic feet, or about 19,150 gallons. A deeper pool with a 6 ft average holds about 23,000 gallons.
How many gallons is a 24 foot round pool?
At 4 ft of water, about 13,500 gallons. At 4.5 ft, about 15,200 gallons.
How much shock do I add to my pool?
For a routine shock, 1 lb of 65 percent cal-hypo per 10,000 gallons raises free chlorine about 7 ppm, so a 20,000 gallon pool takes 2 lb. Broadcast it across the deep end with the pump running; on a vinyl liner, dissolve it in a bucket first so the granules do not bleach the floor. Test in the morning and swim once free chlorine is under 5 ppm.
How much does the water in a pool weigh?
Water weighs 8.34 lb per gallon, so a 20,000 gallon pool holds about 167,000 lb, or 83 tons, of water.
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