Pool Volume Calculator: How Many Gallons Is My Pool?

Almost every pool decision starts with one number: how many gallons your pool holds. Chemical doses, salt additions, shock amounts, pump and heater sizing, and running-cost estimates all depend on it — get the volume wrong and every dose downstream is wrong too. Use the calculator above to get it right, then read on for how it works.

How the calculator works

Enter your pool's shape and measurements — length, width or diameter, and depth — and the tool applies the correct formula for a rectangular, round, oval, or irregular pool to return your gallons. The math differs by shape (a round pool isn't just length times width), which is exactly why a calculator beats guessing. Measure in feet, and measure the actual water dimensions, not the deck.

Getting average depth right

The input people get wrong is depth. If your pool has a shallow and a deep end, use the average depth — typically the shallow depth plus the deep depth, divided by two — not the deepest point. For a flat-bottomed pool, the depth is the same throughout. An honest average depth is what makes the gallon estimate accurate, since a sloped floor holds far less than the deep end alone would suggest.

Why it matters and how to use the number

Once you have your volume, keep it handy — every dosing calculator and chemical label asks for it. When you're uncertain, round conservatively for chemical dosing: it's safer to under-dose, circulate, and retest than to overshoot and have to correct back. A slightly low estimate means you add a bit less and sneak up on the target, which is always the safer direction with pool chemicals. Save the number; you'll use it constantly.