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Pool size

Pool Volume Calculator

Work out how many gallons your pool holds from a few tape-measure readings. Every chemical dose depends on this number.

What you'll need (3)
  • A tape measure (25 ft or longer is easiest)
  • Your pool's shape
  • Water depth at the shallow and deep ends
Units
Pool shapePick the closest match. Freeform lets you enter a measured area.
Surface measurements

Measure the water surface, inside wall to inside wall, not the deck or coping.

The longest straight measurement. Example: 32.
Measured across the middle. Example: 16.
Water depth

Measure to the water line, not the top of the wall. Above-ground pools are usually filled about 6 in. below the top.

Is the floor sloped?
Water depth at the shallow end. Example: 3.5.
Water depth at the deepest point. Example: 8.

Your result

Estimate

Your result will appear here

Enter your pool's measurements and depth to see how many gallons it holds.

How to measure your pool

You need two things: the surface area of the water and its average depth. Measure the water itself, from inside wall to inside wall. Deck, coping and the top rail of an above-ground pool don’t count.

Where to measure a poolTop view of a rectangular pool with length and width arrows, and a side view showing shallow-end and deep-end water depth measured from the water line to the floor.Top viewLengthWidthMeasure inside wall to inside wallSide viewwater lineShallowDeepAverage depth = (shallow + deep) ÷ 2
Measure the water, not the deck. For depth, measure from the water surface to the floor.
  1. Length and width. For a rectangle, measure the longest side and then straight across the middle. For an oval, measure the longest and widest points.
  2. Round pools. Measure the diameter: straight across, through the center. A pool sold as “24 ft round” is 24 ft across.
  3. Depth. Measure from the water surface down to the floor. In a sloped pool, take one reading at the shallow end and one at the deepest point.

The formulas we use

Every shape follows the same idea: gallons = surface area × average depth × 7.48, because one cubic foot holds 7.48 US gallons.

Shape Surface area Notes
Rectangle length × width Exact for straight walls.
Round 3.1416 × (diameter ÷ 2)² Exact for a circle.
Oval 3.1416 × (length ÷ 2) × (width ÷ 2) Treats the pool as an ellipse. Pools with straight sides and round ends hold slightly more.
Kidney 0.45 × (A + B) × length A pool-industry approximation. A and B are the widths of the two rounded ends.
Freeform your measured area Split the pool into rectangles and circles, work out each, and add them up.

Average depth for a sloped floor is (shallow depth + deep depth) ÷ 2. That assumes the floor slopes evenly. A diving pool with a steep “hopper” holds less than this suggests, so treat the result as an upper bound.

Worked example

A 16 × 32 ft rectangle with 3.5 ft at the shallow end and 8 ft at the deep end:

  • Surface area: 16 × 32 = 512 sq ft
  • Average depth: (3.5 + 8) ÷ 2 = 5.75 ft
  • Volume: 512 × 5.75 × 7.48 = about 22,000 gallons

What to do with your number

Pool chemicals are dosed per gallon, so this is the number to type into every other calculator. A 10% error in volume gives a 10% error in every dose. That’s usually fine, because you should add part of a dose and retest anyway.

Don’t over-think precision. Rounding to the nearest 500 gallons is plenty for chemistry. If you ever drain and refill, a water-meter reading is the best real-world check.

Assumptions and limitations

  • Assumes vertical walls and a floor that slopes evenly between the two depths you enter.
  • Diving wells (hopper bottoms), wide steps, benches and sun shelves change the real volume, so treat the result as an estimate.
  • Kidney shapes use the industry approximation 0.45 × (A + B) × length. For an unusual shape, the freeform option with a measured area is more accurate.
  • Measurement error carries straight through: being 6 inches off on the depth of a 5-foot pool changes the result by 10%.

Common questions

How many gallons are in a 24-foot round above-ground pool?

At a typical 4.5 ft (54 in.) water depth, a 24 ft round pool holds about 15,200 gallons. At 4 ft of water it's about 13,500 gallons. Water depth, not wall height, is what counts.

How many gallons is a 16 × 32 inground pool?

With a shallow end of 3.5 ft and a deep end of 8 ft (an average depth of 5.75 ft), a 16 × 32 ft rectangle holds about 22,000 gallons. A hopper-bottom diving pool of the same size usually holds somewhat less.

Why do other calculators give slightly different answers?

Many use rounded shortcuts like 7.5 gallons per cubic foot or 5.9 × diameter² × depth for round pools. We use the exact 7.48 gallons per cubic foot and the true area of a circle, so our numbers can differ by about 0.5%. For chemical dosing, that difference doesn't matter.

Can I find my pool's volume from my water bill?

If you filled the pool from empty on a metered supply, the usage for that billing period (minus your normal household use) is a good check. Water bills often use units of 100 cubic feet (CCF); multiply CCF by 748 to get gallons.

Sources and methodology references

  1. NIST Special Publication 811: Guide for the Use of the International System of Units (Appendix B conversion factors), National Institute of Standards and TechnologyExact definitions of the US gallon (231 in³), so 1 ft³ = 7.4805 gal and 1 gal = 3.7854 L.

Published October 2, 2026. Results are estimates. See how our calculators work.

Spotted a wrong result or an outdated source? Report a problem with this calculator.

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