Pool Volume Formula — Complete Guide

Pool Volume Formula Quick Reference — All Shapes

Every pool volume formula follows one pattern: surface area × average depth = cubic feet, then multiply by a conversion constant. The shape only changes the area step. Use the table below as a cheat sheet, then read the detailed sections for worked examples and constant explanations.

All formulas output cubic feet. Multiply by 7.48052 for US gallons or by 28.3168 for litres. For metric pools (metres), multiply cubic metres by 1,000 for litres.

For an instant result in any shape, use the pool volume calculator on the homepage.

Why Pool Shape Determines the Formula

Every pool volume calculation has three steps:

1. Calculate surface area — this is the only step that changes by shape.
2. Multiply by average depth — gives volume in cubic feet (or cubic metres).
3. Multiply by 7.48052 — converts cubic feet to US gallons. Use 28.3168 for litres.

A rectangle's area is length × width. A circle's area is π × r². An ellipse's area is length × width × π ÷ 4. A kidney's area is approximated with a 0.45 shape factor. The depth and conversion steps stay the same in every case — only the area geometry changes.

The constant 7.48052 exists because 1 cubic foot holds exactly 7.48052 US gallons. Many online guides round this to 7.5, which introduces a 0.27% error — roughly 22 extra gallons on an 8,000-gallon pool. That error is enough to affect chlorine dosing accuracy, so this page uses the precise value throughout.

Rectangular Pool Volume Formula

The constant 7.48052 converts cubic feet to US gallons. One cubic foot equals 7.48052 US gallons — this is a fixed unit conversion, not an approximation. Using 7.5 instead adds roughly 22 gallons of error on an 8,229-gallon pool.

The rectangular formula is the simplest pool volume equation — no shape factor needed because the cross-section is a true rectangle. For pools with a sloped floor, use the average depth method below. Enter your dimensions into the rectangular pool volume calculator or the square pool volume calculator to skip the arithmetic.

Round Pool Volume Formula

Above-ground pool manufacturers print outer frame dimensions on the box — the inner water diameter is typically 6–8 inches smaller per side. Using box dimensions overstates volume by 8–12% and produces chlorine dosing errors of one full dose unit per treatment.

Measure the inner wall-to-wall diameter across the centre of the pool at the waterline for the most accurate result. For an instant calculation, enter your diameter and depth into the round pool volume calculator. Pre-computed volumes for common sizes are listed in the pool volume by size reference table.

Oval Pool Volume Formula

The constant 0.7854 equals π ÷ 4 (3.14159 ÷ 4). It converts the area of a bounding rectangle into the area of the ellipse inscribed inside it. The oval formula is identical to the round formula except it uses two axes — length and width — instead of squaring a single diameter. The result is about 21.5% less volume than a rectangle of the same dimensions. Enter your measurements into the oval pool volume calculator for an instant result.

Kidney and Irregular Pool Volume Formula

The constant 0.45 is not a geometry constant — it is an empirical shape factor that estimates the usable area of a typical kidney shape as a fraction of its bounding rectangle. Pools with an aggressive indentation hold closer to 0.42; pools with a mild curve hold closer to 0.48. Actual volume varies by 3–5% depending on the curve.

Enter your measurements into the kidney pool volume calculator for an instant result. For highly irregular shapes, try the freeform pool volume calculator.

Triangular Pool Volume Formula

A triangle's area is exactly half the area of its bounding rectangle. The ÷ 2 in the formula accounts for this — no other shape constant is needed.

Enter your dimensions into the triangular pool volume calculator for an instant result.

Multi-Section Pools — L-Shaped, T-Shaped, Figure-8

Split the pool into simple shapes, calculate each section separately, then add the results. This works for L-shaped, T-shaped, figure-8, and any other compound layout.

T-shaped pools split into three rectangles. Figure-8 pools split into two circles (or ovals). The method is always the same: break the complex shape into pieces you can calculate, then add. Use the L-shaped pool volume calculator, T-shaped pool volume calculator, or figure-8 pool volume calculator for an instant result.

How to Calculate Average Depth for Variable Depth Pools

Average depth = (shallow end + deep end) ÷ 2. A pool with a 3.5 ft shallow end and a 7 ft deep end has an average depth of (3.5 + 7) ÷ 2 = 5.25 ft. Use 5.25 ft in place of D in any formula listed on this page.

This method works for pools with a single uniform slope from shallow to deep. For pools with a multi-slope profile — such as a shallow shelf that drops to a deep end — split the pool into zones, calculate each zone’s volume separately, and add the results.

Always measure water depth from the waterline to the pool floor — not total wall height. Wall height includes freeboard (the dry section above the waterline), which overstates volume by 4–8 inches and throws off chemical dosing calculations.

Above-ground pools have flat floors and do not need average depth. Enter the actual water depth directly.

Pool Volume Conversion Reference

Use the table below to convert between volume units after calculating cubic feet. All constants are exact or rounded to 5 significant figures.

Conversion constants are exact or rounded to 5 significant figures. Use 7.48052 for US gallons — not 7.5 (introduces 0.27% error).

For unit-specific calculators, see the pool volume calculator in gallons and the pool volume calculator in litres. For chemical dosing based on your pool’s volume, see the pool volume chemical dosing guide.

When to Use a Shape-Specific Pool Volume Calculator

Manual formulas work well for standard geometry — rectangles, circles, ovals, and basic kidney shapes with predictable proportions. For complex or decorative pool designs, a dedicated calculator gives a faster and more accurate estimate.

Pools that benefit from a shape-specific calculator include: all shapes overview, grecian, roman, lagoon, D-shaped, hexagon, octagon, hot tub, plunge pool, and infinity-edge designs.

If you know the pool shape but not the formula, start with the pool volume by shape guide to find the right calculator.