How many gallons is your pool?

How do I calculate how many gallons are in my pool?

Multiply length × width × average depth to get cubic feet, then multiply by 7.48. A 16 × 32 ft pool that goes from 3½ to 8 ft deep averages 5.75 ft: 16 × 32 × 5.75 = 2,944 cubic feet, or about 22,023 gallons.

How do I find the volume of a round pool?

Use 3.1416 × radius² × water depth. A 24 ft round above-ground pool with 4½ ft of water: 3.1416 × 12 × 12 × 4.5 = 2,036 cubic feet, or about 15,228 gallons.

How do I calculate an oval pool?

Multiply 3.1416 × length × width ÷ 4 × depth. A 15 × 30 ft oval with 4 ft of water holds 1,413.7 cubic feet, or about 10,575 gallons.

How do I find the average depth?

Add the shallow and the deep end and divide by 2. If most of the pool is shallow and only a small part is deep, the true average is closer to the shallow depth — measure at a few spots and average them for a better figure.

How long will it take to fill my pool?

Divide the gallons by your hose's flow in gallons per minute, then by 60 for hours. 22,023 gallons at 10 GPM takes about 36.7 hours. Time a bucket to find your real flow with the GPM calculator.

How many gallons is a 15 × 30 ft pool that is 4 ft deep?

15 × 30 × 4 = 1,800 cubic feet, and 1,800 × 7.48052 = 13,465 gallons, or about 50,970 liters.

How the volume is built up

The calculator multiplies the floor area of the water surface by the average depth. A rectangle has area length × width, a round pool π × (diameter ÷ 2)², and an oval π ÷ 4 × length × width. The average depth is the mean of the shallow and deep ends, which is exact for a floor that slopes evenly from one to the other. One cubic foot is 7.48052 US gallons (1 gallon is 231 cubic inches), and one gallon is 3.785411784 liters.

Worked examples

A 20 × 40 ft rectangle sloping from 3.5 ft to 8.5 ft averages 6.0 ft, so it holds 20 × 40 × 6.0 = 4,800 ft³, which is 35,906 gallons. The same footprint at a constant 6.0 ft depth gives 4,800 ft³, the same volume, which shows that only the average depth counts. An 18 ft round pool with 4 ft of water holds 1,018 ft³ or 7,614 gallons, and a 12 × 24 ft oval at 4 ft holds 905 ft³ or 6,768 gallons.

Common mistakes

Using the wall height of an above-ground pool instead of the depth of the water overstates the volume, as most pools run a few inches below the top. Using the deepest point as the depth does the same for in-ground pools. A pool with a pronounced deep end or a hopper bottom is not an even slope, so take depth readings at several spots, and average them; the simple mean of shallow and deep is only as good as that assumption.

Sources: geometry of the rectangle, circle and ellipse as in OpenStax Prealgebra 2e (geometry chapter); the conversion from cubic feet to US gallons (7.48052) and the gallon definition from NIST Handbook 44 and NIST SP 811. Related: pool salt calculator, pool chlorine calculator, pond calculator and tank volume calculator.