Pool Volume Calculator: Measure Your Pool in Gallons

This calculator estimates your pool’s water volume from its shape and measured dimensions. Enter the pool dimensions in feet and choose a shape; it returns an estimated volume in US gallons and liters for planning a fill or checking treatment instructions.

Formula

For a rectangular pool, volume in US gallons = length × width × average water depth × 7.48052. For a circular pool, use π × (diameter ÷ 2)² × average water depth × 7.48052. For an oval pool, this calculator treats the shape as an ellipse: π × length × width ÷ 4 × average water depth × 7.48052. Liters = US gallons × 3.78541.

Length, width, diameter, and depth are in feet; the area is in square feet, and multiplying by depth gives cubic feet. There are approximately 7.48052 US gallons in one cubic foot. The selector makes the calculator apply the matching area formula; for circular pools, enter the diameter as both length and width. For an oval pool, enter its longest and shortest dimensions.

Worked Example

Using the default values—rectangular, 20 ft long, 10 ft wide, and 5 ft average water depth:

1. Find the pool’s volume in cubic feet: 20 × 10 × 5 = 1,000 cubic feet.
2. Convert to US gallons: 1,000 × 7.48052 = 7,480.52 gallons.
3. Round to the calculator’s displayed precision: 7,481 US gallons.
4. Convert to liters: 7,480.52 × 3.78541 = 28,316.8 liters, or about 28,317 liters.

The estimate is useful for understanding approximate capacity. Actual volume can differ because of steps, benches, sloped floors, curved walls, or dimensions that were rounded.

What You’ll Need

• A tape measure or another reliable way to measure the pool’s inside dimensions.
• A note of the pool’s shape and its length, width or diameter, and water depth.
• A calculator, or the fields above. Measure in feet for this calculator; convert metric measurements before entering them.

Step-by-Step

1. Choose the pool shape. Select rectangular for a rectangular pool, circular for a round pool, or oval for an elliptical pool. If the outline is irregular, use the closest shape for a rough estimate and consider dividing it into simpler sections.
2. Measure inside the pool. Measure from the inside wall to the opposite inside wall, not from the outside edges. For a rectangle, record the longest length and the perpendicular width. For a round pool, measure straight across through the center. For an oval, record the longest axis and the width across its widest point.
3. Measure water depth at several places. Measure vertically from the water surface to the floor. For a flat-bottomed pool, one depth may be adequate. If the floor slopes, take readings at the shallow, middle, and deep sections, then calculate an average weighted to the size of each section. A simple average is only a rough estimate when sections differ greatly in length or area.
4. Use water depth, not total wall height. Measure the actual distance from the waterline to the floor. If the pool is partly filled, use its current water depth to estimate the water currently in it; use the intended fill level to estimate capacity at that level.
5. Enter the measurements in feet. Type length, width or diameter, and average water depth. If you measured in inches, divide by 12 to get feet. If you measured in meters, multiply by 3.28084 to convert to feet. Keep all entered dimensions in the same unit.
6. Read both outputs. The first result is the estimated volume in US gallons; the second is the equivalent in liters. The displayed gallons are rounded to a whole gallon, so use the unrounded estimate when available if you need a more precise conversion.
7. Check unusual pool features. For substantial steps, ledges, benches, or a sharply sloped floor, calculate the main body and features separately where possible. Add their volumes, or subtract solid structures that displace a significant amount of water.

Common Mistakes

• Mixing units: Entering a width in inches and a length in feet makes the result incorrect. Convert every measurement to feet first.
• Using the wrong dimensions: A round pool needs its diameter, not its radius. An oval needs its full length and full width, not half-dimensions.
• Using the deep end as the average: This overestimates a pool with a shallow area. Measure multiple points and estimate a representative average depth.
• Measuring outside the pool: Outer dimensions include wall thickness and can inflate the estimate. Measure the water area inside the walls.
• Assuming every pool is a perfect shape: A kidney-shaped pool or one with large built-in features will not match a simple rectangle, circle, or ellipse exactly.
• Rounding too early: Keep decimals during conversions and round only the final result. A small depth error affects the whole calculated volume.

Tips

• Write down each measurement with its unit as you take it, and repeat measurements that seem inconsistent.
• For a sloped rectangular pool with a fairly even slope, average the shallow and deep depths: (shallow depth + deep depth) ÷ 2. For more complex floors, average sections according to their relative area.
• For an L-shaped or irregular pool, split the water area into rectangles and/or circles, calculate each section’s volume using its own average depth, then add the results.
• Use the estimate as a starting point, not an exact water-meter reading. For filling, a meter or a recorded delivery volume can provide a more direct measurement.
• If you need cubic meters, convert liters to cubic meters by dividing by 1,000. One cubic meter equals 1,000 liters.

Troubleshooting

The result seems much too large or small: Check that the selected shape is right and that all dimensions are in feet. Confirm that you entered diameter, rather than radius, for a circular pool, and that depth means water depth.

The pool has a slope or deep end: Do not use the deepest point for the entire pool. Take depth readings by section, estimate each section’s average depth, and calculate the sections separately if the slope is pronounced.

The pool is kidney-shaped or has extensive steps: The built-in formulas only approximate common shapes. Divide the outline into manageable geometric sections, estimate each section’s volume, and add them. Small ledges may not meaningfully change the estimate, but large steps and benches displace water.

The calculator does not accept a measurement: Check that it is a positive number, remove unit symbols, and convert the measurement to feet before entering it. Do not type a comma as a decimal separator.

Frequently Asked Questions

How do I calculate pool volume by hand?
Use the appropriate area formula, multiply by average water depth to get cubic feet, then multiply by 7.48052 for US gallons. For liters, multiply gallons by 3.78541.

How do I find the average depth of a sloped pool?
Measure water depth at several representative points. For a simple, even slope, average the shallow and deep readings; for uneven slopes, estimate and calculate sections separately.

Is a US gallon the same as an imperial gallon?
No. This calculator reports US gallons. One US gallon is about 3.785 liters; an imperial gallon is about 4.546 liters.

Can I use meters instead of feet?
Convert each measurement to feet before entering it: meters × 3.28084 = feet. Alternatively, calculate cubic meters directly, then multiply by 1,000 for liters.

Does this estimate include steps and benches?
It does not model them separately. Large features reduce the amount of water the pool holds compared with a simple-shape estimate, so calculate their volume separately for a closer result.

How accurate is the pool volume estimate?
Accuracy depends on the shape, depth measurements, and features. A regular pool with careful measurements can be estimated well; irregular outlines and sloped floors require section-by-section calculations for better results.

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sel shape | Pool shape | Rectangular=1, Circular=2, Oval=3
in length | Length | ft | 20 | 0
in width | Width or diameter | ft | 10 | 0
in depth | Average water depth | ft | 5 | 0
out gallons | Estimated volume | US gal | shape * length * width * depth * 7.48052 + (1-shape) * pi * (width/2)^2 * depth * 7.48052 + (shape-1) * pi * length * width * depth / 4 * 7.48052 | 0
out liters | Estimated volume | L | gallons * 3.78541 | 0