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Pool Volume Calculator

Find how many gallons or liters of water a rectangular, round, oval or kidney-shaped pool holds.

Level: Grades 7–8

  • Common Core standard 7.G.B.6Solve real-world and mathematical problems involving area, volume and surface area of two- and three-dimensional objects composed of triangles, quadrilaterals, polygons, cubes, and right prisms.
  • Common Core standard 8.G.C.9Know the formulas for the volumes of cones, cylinders, and spheres and use them to solve real-world and mathematical problems.
Printable worksheet

Pool Volume Calculator

Inputs
Measurements in
Pool shape
Depth

The longest dimension of the water surface.

Result

Pool volume

22,023 US gal

The pool holds about 22,023 US gallons (83,365 liters) of water.

In liters
83,365 L
In cubic feet
2,944 ft³
Surface area
512 ft²
Average depth
5.75 ft

See the step-by-step solution ↓

Step-by-step solution

  1. Find the area of the water surface: length times width

    32×16=512 ft²

  2. Average the shallow and deep ends, since the floor slopes evenly between them

    3.5+82=5.75 ft

  3. Multiply the surface area by the average depth to get the volume of water

    512×5.75=2,944 ft³

  4. Convert to liters (1 ft³ = 28.316846592 L)

    2,944×28.316846592=83,364.796367 L

  5. Convert to US gallons (1 US gal = 3.785411784 L)

    83,364.7963673.785411784=22,022.649351 US gal

Test yourself

20 quick questions built from this calculator's formula: work out results, predict what happens when an input changes, and work backward from an answer. Every answer comes with the working.

What this calculator does

Find out how many gallons of water your pool holds. You need that number to fill the pool and to pick the right pump, heater or filter. Above all, you need it to add the right amount of chemicals. Their labels give doses per thousand gallons or per ten thousand liters. Enter the shape of the water surface and its depth. The calculator gives the volume in US gallons, liters, and cubic feet or meters.

It handles four common shapes. Rectangles and circles are exact. Ovals are treated as true ellipses, a smooth stretched-circle shape. Kidney pools have no single formula, so the calculator uses a rule of thumb pool builders use. Some floors slope from a shallow end to a deep end. For those, the calculator uses the average of the two depths. That's exact when the slope is steady.

Where it's used

Why this math matters outside the classroom:

  • Filling a pool. A 32 × 16 ft pool averaging 5 ft deep holds 2,560 ft³, about 19,150 US gallons.
  • Round pools. A 24 ft round pool filled 4 ft deep holds π × 12² × 4 ≈ 1,810 ft³, or about 13,500 gallons.
  • Chemical dosing. Pool owners need the volume in gallons because many treatment labels give doses per 10,000 gallons.
  • Water delivery. Homeowners compare a truck delivery with filling from a hose by first knowing how many gallons the pool takes.
  • Sloped floors. For a pool running from 3 ft to 8 ft deep, the average depth of 5.5 ft is used in the volume.

Grade level and standards: Grades 7–8; Common Core State Standards for Mathematics 7.G.B.6, 8.G.C.9. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.

How to use it

  1. Choose whether you are measuring in feet or meters.
  2. Pick the shape that best matches the water surface.
  3. Choose one depth for a flat-bottomed pool. For a sloped one, choose shallow and deep depths.
  4. Enter the dimensions and read the volume in gallons and liters.

What the inputs mean

Length
The longest dimension of the water surface.
Width at the narrow end
For a kidney pool, measure straight across the narrower end and the wider end, each at its widest point. Then measure the overall length from end to end.
Water depth
Measure to where the water line sits. That's usually several inches below the top of the wall or the coping (the rim around the edge).
Shallow-end water depth
Use the water depth at the shallow end and at the deepest point. A pool with a steep drop into a deep diving well holds less than the simple average suggests. See the limitations below.

Formula and method

rectangle: area = length × width
round: area = π × (diameter ÷ 2)²
oval: area = π × (length ÷ 2) × (width ÷ 2)
kidney (approx.): area = 0.45 × (narrow width + wide width) × length
volume = area × average depth;  average depth = (shallow + deep) ÷ 2
1 ft³ = 28.316846592 L;  1 US gallon = 3.785411784 L (about 7.48 gal per ft³)

The calculator treats the pool like a box with straight sides. Its volume is the surface area (the size of the water's top) times the average depth. π (pi) is about 3.1416, and the small ² means a number times itself. When the floor slopes evenly from one end to the other, the average of the shallow and deep depths gives the exact volume.

To get liters, cubic feet (ft³) are multiplied by the exact factor 28.316846592. Liters become US gallons by dividing by 3.785411784. In metric, one cubic meter (m³) is 1,000 liters (L).

Worked example

A 16 ft × 32 ft rectangular in-ground pool is 3.5 ft deep at the shallow end and 8 ft at the deep end.

  1. Surface area: 32 × 16 = 512 ft².
  2. Average depth: (3.5 + 8) ÷ 2 = 5.75 ft.
  3. Volume: 512 × 5.75 = 2,944 ft³.
  4. Liters: 2,944 × 28.316846592 = 83,365 L.
  5. Gallons: 83,365 ÷ 3.785411784 = 22,023 US gallons.

Result: The pool holds about 22,023 US gallons, or 83,365 liters.

Understanding the result

Chemical dosing charts usually give a dose per 10,000 gallons or per 10 m³. Scale the dose to your result rather than guessing.

Pump turnover is the time a pump takes to move all the water through once. Divide your gallons by the pump's flow in gallons per minute. That gives the turnover time in minutes.

Assumptions and limitations

  • The walls go straight up and down, so the water surface and the floor have the same outline.
  • A sloped floor falls evenly from the shallow end to the deep end.
  • Ovals are true ellipses, and kidney pools follow the 0.45 rule of thumb.
  • Some pools have a separate deep diving hopper (a deep pit), wide steps, benches or sun shelves. They differ from the simple model. Split them into sections for a closer figure.
  • Many above-ground pools sold as oval have straight sides with rounded ends. They hold more than an ellipse of the same length and width. Treat that shape as a rectangle plus one circle.
  • The kidney result is an estimate, because real kidney outlines vary widely.

Frequently asked questions

How many gallons are in a cubic foot of water?

About 7.48 US gallons. A US gallon is set at 231 cubic inches, and a cubic foot is 1,728 cubic inches. So 1,728 ÷ 231 ≈ 7.4805.

How do I measure a pool with a sloped bottom?

Measure the water depth at the shallowest point and at the deepest point. Then use the average. Sometimes the floor has a sharp break, such as a shallow area that suddenly drops into a deep end. In that case, work out the two sections separately and add them.

How many gallons does a round above-ground pool hold?

Multiply π (about 3.1416) by the radius squared, then by the water depth. The radius is half the width across. That gives cubic feet; multiply by about 7.48 for gallons. A 24 ft round pool with 4.5 ft of water holds about 15,229 gallons.

Why does my pool's stated capacity differ from this result?

Makers often quote capacity filled to a set level. They may also include or leave out steps and rounded corners. Water rarely reaches the very top of the wall. So measuring your actual water depth gives the most useful number.

How this calculator is checked

Method: Prism volume (surface area × average depth); circle and ellipse areas; kidney area by the common 0.45 × (A + B) × L trade approximation; exact US gallon (231 in³). The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

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