Pool Volume Calculator

Estimate water volume from the pool’s inside dimensions and actual water depth. Choose a flat bottom or an evenly sloping floor, and subtract known displacement if needed.

Pool plan shapeRounded-end rectangles, kidney pools and freeform shapes are not true ellipses.

Dimension unitsLength, width and depths use this unit. Changing units converts values.

Length or circle diameterftMeasure the inside water surface, not the outside wall.

WidthftFor an oval, use its maximum short-axis width. Not used for a circle.

Depth modelThe endpoint average is valid for this idealized even slope. For multiple floor sections, calculate their volumes separately.

Flat / mean / shallow water depthftMeasure from the waterline to the floor. In flat/mean mode, enter your known area-weighted mean depth here.

Deep-end water depthftUsed only for the even-slope model. Must not be shallower than the first depth.

Volume unitsAlso sets the unit for the displacement input; switching converts that value.

Known displaced volumeUS galSubtract the submerged volume of steps, benches or other solid features not already reflected in your dimensions.

Measured water fill rate (optional)US gal/minSet 0 to omit time. Assumes a constant flow and a complete fill from empty.

Fill-rate units

Calculation results

Estimated water volume

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How to use this calculator

Choose an appropriate shape

Rectangle uses length × width. Circle uses its diameter. Oval means an ellipse, not every pool described commercially as oval.

Use water dimensions

Measure inside the pool at the waterline and use water depth, not wall height. Steps and benches occupy some of that volume.

Describe the floor

For a flat bottom use one depth. For a uniformly sloping floor use shallow and deep endpoints. A short deep well needs an area-weighted estimate or separate sections.

Check volume and optional time

Subtract independently measured solid displacement once. A measured fill rate gives an ideal full-fill duration; supply fluctuations and interruptions are not included.

Formula and worked example

Rectangle area = length × width
Circle area = π × diameter² ÷ 4
True ellipse area = π × long axis × short axis ÷ 4
Even-slope mean depth = (shallow depth + deep depth) ÷ 2
Water volume = area × mean depth − displaced volume
1 US liquid gallon = 0.003785411784 m³ exactly
Ideal fill time = water volume ÷ constant fill rate

A 30 × 15 ft rectangular pool with an evenly sloping floor from 3 to 7 ft has a mean depth of 5 ft. Its idealized volume is 2,250 ft³, or about 16,831.17 US gallons (63,712.90 liters), before steps or benches are deducted. At a constant 10 US gallons per minute, a complete fill takes about 28.05 hours.

Volume of a 30 × 15 ft rectangular pool

Ideal rectangular geometry with no displaced volume. These examples use the exact US-gallon conversion, not the rounded 7.5-gallons-per-cubic-foot shortcut.
Uniform or mean water depth	Volume	US liquid gallons
3 ft	1,350 ft³	10,098.70
4 ft	1,800 ft³	13,464.94
5 ft	2,250 ft³	16,831.17

Frequently asked questions

Is an oval pool always an ellipse?

No. Some oval pools have straight sides with semicircular ends, while others are freeform. This oval mode is a true ellipse. Use a shape-specific or sectional estimate when that does not match your pool.

Why is my answer different from multiplying cubic feet by 7.5?

The 7.5 shortcut is rounded. This calculator uses the exact US liquid gallon definition, equivalent to about 7.48052 US gallons per cubic foot. Measurement and shape uncertainty will often matter more than that conversion difference.

Can I average the shallow and deep ends for any pool?

No. It suits an evenly sloping floor over the modeled symmetric plan. A large shallow area plus a small deep well does not generally have that average depth. Use section volumes or an independently determined area-weighted mean.

Are these US or Imperial gallons?

US liquid gallons. They are not Imperial gallons. Liters and cubic meters are also shown so you can check equipment and product labels using the correct unit.

Can I use this alone to dose pool chemicals?

No. This is a geometric volume estimate, not a treatment or dosing calculator. Confirm the actual water volume and follow the specific product label and appropriate pool-testing guidance.

Methodology and sources

Assumes vertical sides and the selected ideal plan shape. Tapered walls, beach entries, curved floors, attached spas and complex deep ends can need a sectional model or measured fill volume. Fill time assumes an empty pool, constant flow and no leaks or losses. The tool does not size a pump, establish required turnover, approve drainage or calculate chemical doses.

SwimmingPool.com / POOLCORP — pool volume guidance — Waterline measurements, simple geometric volumes and limitations of averaging depth endpoints.
NIST Handbook 44 — measurement tables — Exact US liquid gallon and customary/metric conversions.

Sources checked September 1, 2026. Referenced organizations do not endorse Efficienco. Unit conversions retain full precision until display; displayed water quantities are estimates, not measured capacity.