How do I calculate cubic feet of a swimming pool?

Rectangular pool: length × width × average depth (in feet). Round pool: π × radius² × average depth. For pools with a deep end, use the average of the shallow and deep depths.

How many gallons are in 1 cubic foot of pool water?

7.48052 US gallons per ft³. Multiply your cubic feet by 7.48 to get gallons.

What is the average depth of a pool with a deep end?

Average depth = (shallow end + deep end) ÷ 2. So a pool 3 ft shallow / 8 ft deep has an average depth of 5.5 ft. Use this in the volume formula.

How big a pump do I need for my pool?

Sized to turn over the pool 1–2 times per day. Required GPM (gallons per minute) = (gallons × 2) ÷ 480 minutes (8 hours). A 20,000 gallon pool: 20,000 × 2 ÷ 480 ≈ 83 GPM.

How much does it cost to fill a swimming pool?

At $5–10 per 1,000 gallons of municipal water, a 20,000 gallon pool costs $100–200 to fill. Trucked-in water runs $200–400 per 5,000 gallons.

Pool Cubic Feet Calculator — Volume & Gallons for Round & Rectangular Pools

How to calculate cubic feet for swimming pool

Pool volume is the foundation for sizing the pump, filter, and chemical doses. The formula depends on shape:

Rectangular: length × width × average depth
Round: π × radius² × average depth
Oval: π × (length ÷ 2) × (width ÷ 2) × average depth
Kidney: approximate as 0.45 × longest length × longest width × depth

Average depth = (shallow end + deep end) ÷ 2. For pools with a sloped floor, this approximation is within 1–2% of the true volume.

Worked examples

Example 1: A 16 × 32 ft rectangular pool, 3 ft shallow / 8 ft deep

Average depth: (3+8)/2 = 5.5 ft. 16 × 32 × 5.5 = 2,816 ft³ ≈ 21,065 gallons.

Example 2: A 24 ft round above-ground pool, 4 ft uniform depth

π × 12² × 4 ≈ 1,810 ft³ ≈ 13,538 gallons.

Example 3: A 12 × 24 ft oval pool, 4 ft depth

π × 6 × 12 × 4 ≈ 905 ft³ ≈ 6,769 gallons.

Common pool sizes

Pool	Conversion factor	Worked example
12 × 24 ft, 4 ft deep	1,152 ft³	~8,617 gallons
16 × 32 ft, 4 ft deep	2,048 ft³	~15,318 gallons
16 × 32 ft, 3/8 ft (avg 5.5)	2,816 ft³	~21,065 gallons
20 × 40 ft, 4 ft deep	3,200 ft³	~23,938 gallons
20 × 40 ft, 3/8 ft (avg 5.5)	4,400 ft³	~32,914 gallons
24 ft round, 4 ft deep	1,810 ft³	~13,538 gallons
15 ft round, 4 ft deep	707 ft³	~5,290 gallons

Tips and considerations

Filter turnover targets

Residential pools should turn over once every 8–10 hours. Calculate required GPM as: (gallons × 2) ÷ 480 minutes for 2 turnovers per 8-hour run cycle.

Chemical dosing

Most pool chemicals are dosed per 10,000 gallons of water. Knowing exact gallons prevents over-treatment (which fades vinyl liners) and under-treatment (which lets algae bloom).

Common mistakes to avoid

Confusing nominal pool size with actual water volume. A 24-foot round pool is 24 ft outer diameter — the water surface is smaller. Use the inside dimension.
Using maximum depth instead of average depth. Pools with sloped bottoms have very different volumes than rectangular pools. Use average depth.
Forgetting freeboard. A pool is rarely filled to the rim — water level is usually 6–8 inches below the top. Subtract that depth from your calculation.
Mixing US and metric. European pools list cubic meters; US chemicals dose by gallons. Convert before treating.