Pool Gallons Calculator

Pool capacity is one input to chemical and circulation planning. Product strength, current test results, target range, equipment, local code, and operating conditions also matter. Do not assume one universal eight-hour turnover requirement; use the equipment design and applicable health rules.

Measure the water surface at the top of the pool, from inside wall to inside wall. For rectangle and oval pools, take the longest length and the widest width. For a round pool, measure straight across the middle through the deepest point to get the diameter, not the radius. If you only have the radius, double it. For above-ground pools, the manufacturer label inside the rim usually lists the diameter or length and width, which is the easiest place to start.

If your pool has a shallow end and a deep end, you cannot multiply by one depth. Add the shallow end depth and the deep end depth, divide by 2, and use that average. The calculator does this automatically when you fill in both depths. The trick assumes a roughly linear slope from one end to the other, which holds for almost every residential inground pool. For a flat-bottom above-ground pool, just enter the same number in both depth fields, or leave the deep end blank.

Kidney and freeform results are geometric estimates. Actual error depends on the shape, benches, steps, coves, and depth profile, so do not assume a fixed plus or minus 10% accuracy. Use construction records, meter a known fill, or make conservative chemical adjustments confirmed by water testing.

One US gallon is defined as exactly 231 cubic inches. A cubic foot is 12 x 12 x 12 = 1,728 cubic inches. Divide and you get 1,728 / 231 = 7.480519 US gallons per cubic foot. The calculator uses that value to convert pool volume in cubic feet to capacity in gallons. The British imperial gallon is larger (about 6.23 imperial gallons per cubic foot), so make sure your chemical labels list US gallons before you dose.