Pool Volume Calculator
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About Pool Volume
“How many gallons is my pool?” is the first question of every water-chemistry product label and every heater or pump purchase — and most owners inherit a pool without paperwork. Two tape measurements and a depth check recover the number in a minute.
Pick the shape, enter the dimensions and both end depths, and get gallons, liters, cubic meters, and the water's weight. Freeform and kidney shapes: run the closest oval and expect the truth within ~10–15%, or split the outline into simpler shapes and add.
Cylindrical tanks, hot tubs, and barrels have their own tool — the Tank Volume Calculator
The Volume Formulas
Area by shape, times average depth, times the gallons constant:
Average depth = (shallow + deep) ÷ 2 Rectangle: L × W × avg × 7.48 Round: π × (D ÷ 2)² × avg × 7.48 Oval: π⁄4 × L × W × avg × 7.48
Worked example: a 32′ × 16′ rectangle sloping 3′ to 8′ averages 5.5′ deep — 2,816 ft³ × 7.48 = about 21,065 gallons, roughly 176,000 lb of water. That last number is why pools don't get moved and above-grounds need level ground.
Common Pool Sizes in Gallons
Typical builds at typical depths — all computed by this calculator's formula:
| Pool | Avg depth | Volume |
|---|---|---|
| 12 × 24 ft rectangle | 4.5′ | ~9,700 gal |
| 16 × 32 ft rectangle | 4.5′ | ~17,200 gal |
| 18 × 36 ft rectangle | 5′ | ~24,200 gal |
| 15 ft round (above-ground) | 4′ | ~5,300 gal |
| 24 ft round (above-ground) | 4′ | ~13,500 gal |
| 15 × 30 ft oval | 4.5′ | ~11,900 gal |
The classic 16 × 32 in-ground lands near 17,000–20,000 gallons depending on the deep end — which is why “about 20,000” is the default assumption pool stores make when you don't know.
What the Number Is For
Chemistry doses scale directly with volume: chlorine shock, algaecide, pH adjusters, and stabilizer are all labeled per 10,000 gallons, and a salt chlorinator needs pounds of salt proportional to the water it treats. Dosing a 17,000-gallon pool as “about 25,000” chronically overshoots — costume-bleaching, eye-stinging territory — while undershooting invites algae.
Equipment sizing keys off it too: pumps are chosen to turn the full volume over roughly once every 8–12 hours (a 17,000-gallon pool wants ~30+ GPM real flow), and heater sizing starts from the gallons being warmed. Filling costs are the volume in your water rates; evaporation top-ups run inches per week in summer — the calculator's per-inch volume is the surface area × 7.48 ÷ 12.
Frequently Asked Questions
How many gallons is my pool?
Length × width × average depth × 7.48 for a rectangle — a 16 × 32 pool averaging 4.5′ deep holds about 17,200 gallons. Round pools use π × radius² for the area. Enter your shape and dimensions above for the exact figure.
How do I handle a sloped bottom?
Average the two ends: a 3′ shallow and 8′ deep end average 5.5′, which is accurate for the standard straight slope. A pool with a distinct shallow shelf plus a diving well is better split into two rectangles and added.
How many gallons is a 24-foot round pool?
At the typical 4′ of water: about 13,500 gallons (π × 12² × 4 × 7.48). The common above-ground sizes: 15 ft ≈ 5,300 gal, 18 ft ≈ 7,600 gal, 24 ft ≈ 13,500 gal, 27 ft ≈ 17,100 gal at that depth.
Why does chemical dosing need the exact volume?
Because every label doses per 10,000 gallons. Guessing 25,000 for a 17,000-gallon pool over-chlorinates by nearly half every single treatment; guessing low grows algae. One good volume measurement fixes years of dosing.
How much does pool water weigh?
About 8.34 lb per gallon — a modest 17,000-gallon pool holds over 70 tons of water. It's why in-ground pools never move, above-grounds demand truly level compacted ground, and “draining it onto the lawn” needs more thought than it gets.
How much water does evaporation take?
Commonly ¼–½ inch a day in hot dry weather. Each inch of your pool's surface is area × 7.48 ÷ 12 gallons — about 320 gallons per inch on a 16 × 32. If you're topping up much faster than that, suspect a leak, not the sun.
Methodology. This calculator uses standard construction and material-estimation formulas. It is reviewed and maintained by the Vast Calculators editorial team.
Last updated · July 11, 2026
Results are estimates for general use; verify critical figures independently.