Pool Volume Calculator

How to work it out

1. Measure at the water line

   Length and width across the water, not the coping or the deck. For a round pool, put the diameter in both boxes.

2. Measure both depths

   Depth is from the water surface to the floor, not the top of the wall. A flat-bottomed pool has the same figure twice; a sloping pool needs the shallow and deep ends and the average is taken.

3. Write the number down

   Every dose on every chemical label is per 10,000 gallons. Write your volume on the pump housing or inside the equipment cover and you never have to work it out again.

4. Check it against the pump

   A pool should turn its whole volume over in about eight hours. The flow rate needed for that is shown above — worth comparing with your pump's rating.

Gallons in common pool sizes

Rectangular pools with a 3 ft shallow end and a 6 ft deep end, so an average depth of 4.5 ft.

Pool size	Surface area	Gallons
12 × 24 ft	288 sq ft	9,695
14 × 28 ft	392 sq ft	13,196
16 × 32 ft	512 sq ft	17,235
18 × 36 ft	648 sq ft	21,813
20 × 40 ft	800 sq ft	26,930

Round above-ground pools

Filled to 6 in below the top rail, which is where they normally sit.

Diameter	Wall height	Approximate gallons
12 ft	48 in	2,960
15 ft	48 in	4,625
18 ft	52 in	7,295
24 ft	52 in	12,970
27 ft	52 in	16,420

How to work out pool volume

Surface area times average depth gives cubic feet, and a cubic foot of water is 7.48 gallons.

For a rectangle the surface area is length times width. A round pool is 0.7854 times the diameter squared. A kidney or freeform pool is close enough to 0.85 of the rectangle that would enclose it, which is the figure the pool trade uses.

Average depth on a sloping floor

Most in-ground pools have a shallow end, a slope and a deep end. Adding the two depths and halving them is accurate enough for chemical dosing — within a percent or two on a normal hopper bottom.

If your pool has a long flat shallow section and a short deep end, that simple average overstates the volume slightly. Measuring the depth at three points and averaging those is closer.

Why the number matters

Every pool chemical is dosed per 10,000 gallons. Guess the volume 20% high and you under-treat by 20%, which is how people end up chasing cloudy water all summer and adding more of everything.

It also sets the pump you need, the heater size, and how long it takes to fill — a 16 × 32 ft pool is about 17,000 gallons, which is a full day on a garden hose.

How this is worked out

No black box — here is the arithmetic the calculator runs, so you can check it against your own numbers.

1. surface area = length × width × shape factor 1 for a rectangle, 0.7854 for a circle or oval, 0.85 for freeform.
2. average depth = (shallow + deep) ÷ 2 Close enough for dosing on a normal sloping floor.
3. cubic feet = surface area × average depth The volume of water held.
4. gallons = cubic feet × 7.48 US gallons in a cubic foot.

Common questions

How many gallons is a 16x32 pool?

About 17,200 gallons with a 3 ft shallow end and a 6 ft deep end. A flat 4 ft bottom would be about 15,300.

How do I calculate gallons in a round pool?

Diameter × diameter × average depth × 5.9. A 24 ft round pool 4 ft deep holds about 13,500 gallons.

How many gallons in a cubic foot of water?

7.48 gallons. A cubic yard of water is 202 gallons.

Does the pool volume change when the water level drops?

Yes, and by more than people think. Every inch off a 16 × 32 ft pool is about 320 gallons, so dosing from the full-pool figure after a long dry spell overshoots.

How long does it take to fill a pool?

A garden hose delivers roughly 8–10 gallons per minute, so about 30 hours for 17,000 gallons. A water delivery truck carries 5,000–6,000 gallons.

What pump flow do I need?

Enough to turn the whole volume over in eight hours — the figure is shown above. For 17,000 gallons that is about 35 gallons per minute.

How do I measure a freeform pool?

Take the longest length and the widest width, and use the kidney setting, which applies the 0.85 factor pool professionals use for curved shapes.

Where these figures come from

Every figure below is traceable. How we check the numbers explains how they are verified, and the coverage reference collects them all in one place.

• Association of Pool & Spa Professionals guidance — shape factors used for freeform and oval pools
• NIST Special Publication 811 — cubic foot to US gallon and gallon to liter conversions
• Pool equipment manufacturer sizing guides — the eight-hour turnover rule for pump flow

Think a number here is wrong? Tell us — we check every report, correct the page, and date the change. Last checked September 27, 2026.