Swimming Pool Volume: Gallons, Turnover Time, and Pump Flow Rate
October 21, 2026
Knowing how many gallons are in a pool is the starting point for dosing chemicals, sizing a pump and filter, and estimating heating costs. The volume depends on the shape and the average depth. For a rectangular pool, volume in cubic feet is length × width × average depth, and gallons are cubic feet × 7.48. A 16 × 32 foot pool that slopes from 3 feet deep at the shallow end to 8 feet at the deep end has an average depth of 5.5 feet, giving 2,816 cubic feet or about 21,065 gallons.
Pool sizes are often quoted loosely, so measure your own and calculate.
Skip the math and get your answer instantly:
Open the Volume Calculator →Formulas by Shape
Rectangle: L × W × average depth × 7.48. Circle: π × r² × average depth × 7.48. Oval: π × (L ÷ 2) × (W ÷ 2) × average depth × 7.48 (or L × W × average depth × 5.9 as a quick approximation). Kidney or freeform: approximate as an oval with a correction, or use (A + B) × C × 0.45 × depth × 7.48 for a kidney shape with width measurements A and B and length C.
For a round above-ground pool 24 feet across with a water depth of 4.5 feet: π × 12² × 4.5 × 7.48 = 15,228 gallons.
| Pool | Dimensions | Volume (cubic feet) | Gallons |
|---|---|---|---|
| Rectangular in-ground | 16 x 32 ft, 3 to 8 ft deep | 2,816 | 21,065 |
| Round above-ground | 24 ft diameter, 4.5 ft | 2,036 | 15,228 |
| Rectangular small | 12 x 24 ft, 4 ft avg. | 1,152 | 8,617 |
| Round small | 15 ft diameter, 4 ft | 707 | 5,288 |
Average Depth
For a pool with a constant slope from shallow to deep, average depth is (shallow + deep) ÷ 2. If it has a flat shallow section and a flat deep section with a slope between them, calculate each part separately and add the volumes. Many pools have a hopper bottom or a swim-out section, so measure depth at several places with a weighted line.
If you are unsure, an error of 10% in depth gives 10% error in volume, which would affect chemical dosing. Pool professionals can use a flow meter test to verify.
Pump Flow and Turnover
Turnover time is how long it takes to circulate the entire pool volume through the filter once. Most guidelines call for a turnover every 6 to 8 hours for residential pools, and public pools require shorter times. Flow rate (gpm) = volume ÷ turnover time in minutes. For 21,065 gallons and an 8-hour turnover: 21,065 ÷ 480 = 43.9 gpm. For 6 hours: 58.5 gpm.
The pump must deliver that flow against the head loss of the plumbing and filter. Variable-speed pumps can run at a lower speed for longer, which saves a lot of energy, because the power needed falls rapidly as speed drops.
Why Volume Matters for Chemicals
Chemical dosing instructions are given per 10,000 gallons. Adding the wrong amount for a 21,000-gallon pool can leave you with too little sanitizer or too much, which risks skin and eye irritation and equipment damage. Use a test kit to measure free chlorine (commonly 1 to 3 ppm), pH (7.2 to 7.6), alkalinity, and stabilizer, and follow the product label for doses based on your volume. A one-ppm increase in chlorine in 10,000 gallons needs a specific amount of product depending on its strength.
Heating and Water Costs
Volume also determines how much it costs to heat the pool or fill it. Filling 21,065 gallons at a water price of $5 per 1,000 gallons costs about $105. Heating requires about 8.34 BTU per gallon per degree F: raising 21,065 gallons by 10°F needs 21,065 × 8.34 × 10 = 1.76 million BTU, before heat losses. A pool cover cuts evaporation and heat loss substantially.
Frequently Asked Questions
How many gallons are in a cubic foot?
7.48 US gallons.
How do I calculate pool volume?
Multiply length × width × average depth for rectangles, then multiply by 7.48 to get gallons.
What is the right pump flow rate?
Volume divided by the desired turnover time in minutes, commonly 6 to 8 hours.
Why does pool volume matter?
It determines chemical doses, pump sizing, and heating and fill costs.
What is the average depth of a sloped pool?
(Shallow end + deep end) ÷ 2 for a constant slope.