Pool Volume Calculator
Enter your pool's shape and dimensions to get gallons, liters and cubic feet.
Pool Volume
Use this volume in…
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Take the quizHow pool volume is calculated
Pool builders and pool-supply companies use simple constant-multiplier formulas to estimate volume: for a rectangular pool, gallons = length × width × average depth × 7.5. For a round pool, gallons = diameter × diameter × average depth × 5.9. An oval pool uses the same 5.9 multiplier as a round pool, applied to length × width, and is also used here as a reasonable approximation for a kidney-shaped pool.
The 7.5 and 5.9 multipliers come from the fact that a cubic foot of water holds about 7.48 gallons; a rectangular prism uses that number directly, while a cylinder (or oval, which is roughly an ellipse) only fills about 78.5% of its bounding rectangle, which is where 5.9 (7.48 × 0.785, rounded) comes from.
Average depth matters more than either end depth alone. If your pool has a shallow end and a deep end connected by a slope, the true average is very close to (shallow depth + deep depth) ÷ 2 for most residential pool shapes, which is why that is the default here. If your pool has a single uniform depth (common for above-ground pools and small spools), just enter that one number as the average.
Once you know the gallons, you can jump straight to dosing salt, chlorine or shock for that exact volume using the “Use this volume in…” links below the result -- they carry your computed gallons over automatically.
This calculator is sized for pool-scale volumes. If you're instead measuring a spa, use the hot tub gallons & volume calculator, which is tuned for those smaller numbers and links straight into hot tub-scale chemical dosing.
Where these numbers come from
The formulas and default values in this calculator are based on:
- standard pool-industry volume formulas (length x width x avg depth x 7.5 for rectangular pools
- diameter squared x avg depth x 5.9 for round pools), used by pool-supply retailers and pool service companies nationwide
- 1 cubic foot = 7.48 gallons
- 1 gallon = 3.785 liters
These are planning estimates. Test your actual water, follow product labels, and check your equipment manufacturer's guidance before you buy or dose chemicals.
Frequently asked questions
Why do round pools use a different multiplier than rectangular pools?
A round pool is a cylinder, and a cylinder holds less water than a rectangular box with the same width, length and depth -- only about 78.5% as much, since a circle covers 78.5% of the square that contains it. The 5.9 multiplier already builds that percentage in, so you don't need to adjust for it yourself.
My pool has a diving well or a step -- does that change the answer?
A little. A diving well adds volume beyond a simple shallow/deep slope, and steps and benches remove a small amount of volume. For most backyard pools this is within the normal margin of error for a volume estimate (± 5-10%), which is accurate enough for chemical dosing. For an exact number, a pool professional can do a fill-time or fill-meter measurement.
How accurate does my volume need to be for adding chemicals?
Being within about 10% is generally fine -- test strips and test kits are themselves not perfectly precise, and you'll fine-tune with regular testing anyway. It's more important to be consistent: use the same volume figure every time you dose so your adjustments are comparable from week to week.
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