Pool Volume Calculator
Calculate your pool volume in gallons or liters. Supports rectangular, round, oval, and irregular pool shapes.
Pool volume in gallons is length × width × average depth × 7.5 for a rectangle, or diameter × diameter × average depth × 5.9 for a round pool. Both fold in the 7.48 gallons-per-cubic-foot conversion and land within half a percent. Measure average depth to the water line, not the coping. Enter your pool's dimensions above for the exact figure.
Get This Number Right First
Volume is the input every other pool calculation depends on. Chlorine, shock, alkalinity, calcium, CYA, salt — every dose is a rate multiplied by gallons, so an error here does not stay here. It scales into every chemical you add for as long as you own the pool. A 20,000-gallon pool you believe is 15,000 gets 25% under-dosed on everything, forever, and the symptom shows up as chlorine that never holds rather than as an obviously wrong number.
The figure on your build contract, or on the box the pool came in, is a nominal capacity rather than a measurement. It assumes the pool is filled to the brim and that the depth is what the drawing said. Measure it yourself once and write it on the equipment pad in permanent marker.
The formula, and the shortcut
Volume in gallons is surface area × average depth × 7.48 — there are 7.48052 gallons in a cubic foot. This calculator uses the exact figure and real geometry, so a round pool is computed as π × radius², not approximated.
Doing it by hand, the industry shortcuts fold the conversion into a single multiplier: length × width × average depth × 7.5 for a rectangle, and diameter × diameter × average depth × 5.9 for a round pool. Both land within half a percent of the exact answer, which is far tighter than the error in your depth measurement — so use them freely for mental math, and use the calculator when you want the number you will dose against.
Average depth is where people go wrong
Average depth is not max depth, and it is not the depth you swim at. For a pool whose floor slopes evenly from one end to the other, it is the shallow depth plus the deep depth, divided by two. For the common build — a flat shallow section, then a slope, then a flat deep end — that mean overstates the volume, because the flat shallow area covers more of the footprint than the deep end does. Weight it instead: measure the length of each section, work out its own average depth, and combine them by share of the floor.
Measure to the water line, not to the coping. Most pools run four to six inches below the tile, and on a 16 × 32 pool five inches of missing water is close to 1,000 gallons.
Pool Volume Chart
Common rectangular pool sizes at three average depths. Use it to sanity-check your own figure — if your measurement is far from the row that matches your pool, re-check the depth before you re-check the arithmetic.
| Pool size | Surface area | 4 ft avg | 4.5 ft avg | 5 ft avg |
|---|---|---|---|---|
| 12 × 24 ft | 288 sq ft | 8,600 gal | 9,700 gal | 10,800 gal |
| 14 × 28 ft | 392 sq ft | 11,700 gal | 13,200 gal | 14,700 gal |
| 16 × 32 ft | 512 sq ft | 15,300 gal | 17,200 gal | 19,200 gal |
| 18 × 36 ft | 648 sq ft | 19,400 gal | 21,800 gal | 24,200 gal |
| 20 × 40 ft | 800 sq ft | 23,900 gal | 26,900 gal | 29,900 gal |
| 25 × 45 ft | 1,125 sq ft | 33,700 gal | 37,900 gal | 42,100 gal |
Rounded to the nearest 100 gallons — dosing at this scale does not benefit from more precision. Round and oval pools of the same footprint hold roughly 22% less, because a circle covers less area than the rectangle drawn around it.
Freeform and kidney shapes
There is no formula for a shape nobody has a name for. Break the pool into rectangles and half-circles you can measure, work each one out, and add them up — that gets within a few percent, which is inside the noise of your depth measurement anyway. The alternative, if you want it exact, is to read the water meter, drain and refill, and take the difference. That is accurate and expensive, and worth doing only if you were draining the pool regardless.
Once you have a number you trust, take it to the chlorine calculator for routine dosing, the shock calculator when the water turns, or the water balance calculator to work the whole panel in the right order. It also sets your filter and pump sizing — see the filter size calculator for the turnover maths.