Pool Volume Calculator (Litres, m³ & Gallons)

How to calculate pool volume in litres

Multiply the pool’s surface area in square metres by its average water depth in metres — that gives cubic metres — then multiply by 1,000, because one cubic metre holds exactly 1,000 litres. A 10 m × 4 m rectangular pool averaging 1.6 m deep is 10 × 4 × 1.6 = 64 m³, or 64,000 litres. The calculator above runs that same arithmetic for round, oval, kidney and freeform pools, and prints litres, cubic metres, US gallons and cubic feet from one set of measurements.

Switch the Measure in toggle to m and every field, the formula line and the headline turn metric: you type metres, you read litres. Leave it on ft and the same pool reads in US gallons. It is the same calculation either way: the toggle changes what you read, never how the volume is worked out.

The optional fill-cost field follows the toggle too, and it is the one place where that matters for the answer rather than the wording. Water is billed per 1,000 US gallons on a US utility bill and per kilolitre — 1,000 L on a metric one, so the field relabels itself and converts what you type. Enter an AU/NZ tariff of $3.50/kL against the 10 m × 4 m pool below and the fill comes out at about $224, not the $59 you would get by pricing 16,906 gallons at a per-kilolitre rate. Check the label above the field before you type: it always names the basis it is expecting.

Litres, cubic metres, gallons and cubic feet

These four readings are the same water. The conversion factors are definitional, not estimates:

Factors from NIST’s Guide to the SI, Appendix B.9, and the NIST Office of Weights and Measures’ SI Units — Volume. Imperial (UK) gallons are a different unit and appear nowhere on this page: every “gal” here is a US gallon, because that is the unit pool chemistry is written against.

A worked metric example

Take a 10 m × 4 m rectangular pool, 1.2 m at the shallow end and 2.0 m at the deep end. Average depth is (1.2 + 2.0) ÷ 2 = 1.6 m, so the pool is 64 m³. The calculator prints 63,996 L · 64.0 m³ · 16,906 gal · 2,260.1 ft³.

That 63,996 rather than a flat 64,000 is deliberate and worth understanding. The engine converts to US gallons at 7.48 gal/ft³ — the everyday pool-industry figure, and a rounding of the exact conversion NIST’s factors give, which is 1,728 in³ per cubic foot ÷ 231 in³ per US gallon = 7.480519… repeating — so a metric reading comes out about 0.007% low, four litres in sixty-four thousand. We keep the 7.48 pin because it is the constant the dose charts and the rest of this suite are built on, and because four litres is far inside the error of the tape measure that produced the 10 and the 4.

Average depth is where litre counts go wrong

Length and width are easy; depth is where estimates drift. The calculator uses (shallow + deep) ÷ 2 and echoes the average it used in the result, so the assumption is visible before you dose anything corrosive. Leave the deep end blank and the shallow depth is used as-is for a constant-depth pool.

The plain mean assumes the floor slopes evenly from one end to the other. Pools with a long flat shallow shelf and a short deep pocket hold less than the mean implies — for those, switch the shape to Freeform, break the pool into two or three regular parts, and let the tool add them. Measure depth to the water line you actually maintain, not to the top of the coping: every 100 mm of water you are not carrying takes 100 litres per square metre of surface off the real volume — about 4,000 litres on a 10 m × 4 m pool.

The metric formula for each shape

Every shape is surface area × average depth × 1,000 = litres:

• Rectangle — L × W × avg depth × 1,000
• Round — π × (diameter ÷ 2)² × avg depth × 1,000
• Oval — L × W × (π ÷ 4) × avg depth × 1,000, using the two full axes
• Kidney — 0.45 × (width A + width B) × length C × avg depth × 1,000
• Freeform — the sum of the parts you enter

The kidney 0.45 area factor is the standard industry approximation, not a derived constant, and the oval uses the full-axes π/4 convention so the labels and the arithmetic agree. Both are shown substituted with your own numbers in the result, so a tech can sanity-check the figure poolside. If you need the surface figure on its own — for covers, resurfacing or a tile count — the pool surface area calculator stops at square metres. To go a step further and get resurfacing material from the same shell dimensions — bags of plaster, quartz, or pebble — the pool resurfacing material calculator picks up where the surface figure leaves off.

Where the litre figure goes next

Volume is the denominator for everything else you do to the water. Once you have it, carry the same number into the chlorine dose calculator, the shock calculator and the salt calculator — each takes gallons or litres, so the unit you measured in is the unit you can keep working in. Volume also drives turnover: it sets the flow rate your filter and pump have to move, which is where the pool filter size calculator picks up. For the whole chain of water-chemistry decisions in order, the pool water chemistry hub is the map.

If you are opening pools in September or October — the southern-hemisphere season — pinning volume for every account before the first service is the cheapest job you will do all year: every dose, every salt top-up and every turnover figure for the next six months is downstream of it. See working in litres for an Australian or New Zealand opening for the rest of that season’s checklist. Northern-hemisphere operators hit the same moment in April and May.

What this number is not

It is a planning and dosing volume built from a tape measure, a shape approximation and an average depth. It is not an engineering or structural survey volume, not a certified capacity for a regulated commercial pool, and not a substitute for a fill meter when you are billing water. Kidney and freeform results in particular are approximations by construction. Nothing you type leaves your browser, there is no account, and the CSV, print, PDF and copy-as-text exports are all ungated.