🏊 Pool Volume Calculator

What This Calculator Does

This calculator tells you how much water your pool holds. Choose the shape — rectangular or round — enter the dimensions and average depth, and it returns the volume in gallons and liters. It is the single number the rest of pool ownership hangs on: every chemical dose, pump choice, and heating estimate assumes you know your gallons.

Most owners inherit a guess (“about twenty thousand, I think”) and dose chemicals against it for years. Measuring the pool once and computing the real figure takes five minutes and quietly fixes every dose that follows.

The Volume Math for Real Pools

Water volume is geometry times a constant. A rectangular pool is length × width × average depth in feet, giving cubic feet, times 7.48 gallons per cubic foot: 32 × 16 × 5 × 7.48 ≈ 19,150 gallons. A round pool uses πr² for area — an 18-ft round pool 4 ft deep is 3.1416 × 81 × 4 × 7.48 ≈ 7,610 gallons. Liters are gallons times 3.785 for equipment specified metrically.

Average depth is the only judgment call. Constant-depth pools use that depth directly. The classic sloped pool — shallow end to deep end with a steady grade — averages the two ends: (3 + 7) ÷ 2 = 5 ft. Pools with a distinct shallow shelf and a diving well average less neatly; treat each region as its own rectangle, compute separately, and sum, exactly like decomposing an odd room into rectangles. Freeform “kidney” pools approximate honestly at about 0.85 × length × widest width × average depth × 7.48 — an industry rule that acknowledges the curves.

Why Gallons Govern Everything Chemical

Pool chemistry is dosing per volume. Product labels prescribe per 10,000 gallons: a shock treatment might call for one pound per 10,000, so the 19,150-gallon pool above needs just under two pounds — and an owner who believes the pool is 15,000 chronically under-doses by 20%+, which is how persistent algae and cloudy water happen despite “doing everything right.” Chlorine targets, pH and alkalinity adjustments, stabilizer, and salt (for saltwater systems, which need a precise salinity in parts per million) all scale the same way.

The volume error compounds because chemistry is iterative: test, dose, retest. Doses computed against the wrong volume never land where the test predicts, so owners chase readings with correction after correction — frustration that a correct gallon figure ends. It is worth writing the computed volume somewhere permanent (many keep it on the pump-house wall) because every future product label, water-care app, and pool-store consultation will ask for it first. One honest measurement outperforms years of estimating.

Pumps, Heaters, and Turnover

Equipment sizing keys off the same number. The standard circulation target is turning the full volume over in about 8 hours; a 19,000-gallon pool therefore wants roughly 19,000 ÷ 480 minutes ≈ 40 gallons per minute of real flow — the figure to compare against a pump's curve at your plumbing's head, not its box rating. Filters are rated in gallons too, and oversizing a filter (unlike a pump) is generally virtuous, extending cleaning intervals.

Heating is where volume becomes viscerally expensive: raising water temperature takes about 8.34 BTU per gallon per degree Fahrenheit, so lifting the 19,000-gallon pool 10°F requires roughly 1.6 million BTU delivered — hours of heater runtime and a visible energy bill, which is why covers (cutting evaporative loss, the dominant heat drain) repay themselves quickly. Water bills at filling or draining, winterizing antifreeze quantities, and even evaporation top-off estimates all trace back to gallons. Compute it once here; everything downstream gets easier and cheaper.

Quick Tips

• Gallons = area × average depth × 7.48 (round pools: πr² for area).
• Average a sloped pool's ends: (shallow + deep) ÷ 2.
• Chemical labels dose per 10,000 gallons — wrong volume means every dose misses.
• Write the figure down; every product and pool store will ask for it.

Frequently Asked Questions

How do I calculate my pool's gallons?

Surface area times average depth times 7.48 (gallons per cubic foot). A 32 x 16 ft rectangular pool averaging 5 ft deep holds 32 x 16 x 5 x 7.48 ≈ 19,150 gallons. Round pools use πr² for the area.

How do I find the average depth?

For a pool with a shallow and deep end connected by a steady slope, average the two: (shallow + deep) ÷ 2. A 3-ft shallow end and 7-ft deep end average 5 ft. Constant-depth pools just use that depth.

Why does pool volume matter?

Every chemical dose — chlorine, shock, pH adjusters, algaecide — is prescribed per volume, typically per 10,000 gallons. Pump and filter sizing, heater BTUs, and turnover times all key off the same number. Wrong volume means every dose is wrong.

How many gallons are in a cubic foot?

7.48. That constant converts any pool's cubic feet into gallons, and it is why the formula is simply area x depth x 7.48. A liter conversion multiplies gallons by 3.785.

Measured Once, Useful Forever

This calculator runs entirely in your browser, converting dimensions to gallons the moment you type. It needs no account or download and works on any device. Like every tool here, it is free to use as often as you like.

Related Tools

For related math, the liters to gallons converter switches volume units, the BTU calculator handles the heating side, and the square footage calculator measures the deck around it.