Swimming pool volume
A rectangular pool 10 metres by 4, sloping from 1.0 to 2.0 metres, holds 60 cubic metres, which is 60,000 litres or about 13,198 imperial gallons. Surface area times average depth is the whole calculation, and how well it matches your pool depends entirely on the shape of its floor.
Last reviewed 14 August 2026
What this calculator tells you
It converts pool dimensions into a capacity, in the three units a UK pool owner meets, plus the surface area figure the bucket test needs.
- Volume in cubic metres, litres, and imperial gallons
- Surface area in m², which is the input the bucket test runs on
- The average depth it used, so you can see the assumption rather than infer it
This is the one calculator on the site that reports no rate of loss, no daily volume and no cost, because it is not measuring a leak. It measures a pool. The absence is deliberate.
How to take the measurement
Three measurements for most shapes, four for a kidney, and one decision that matters more than any of them.
- Length and width at the water line, not at the coping. The coping overhangs, so measuring across it overstates both.
- The depth at the shallow end and at the deep end, from the water surface to the floor.
- For a kidney, the width at its widest point and at its narrowest, plus the overall length.
The decision is what to enter as the depths, and it is where most of the error comes from. how to measure average depth on a real pool floor covers what to do when the floor is not a uniform slope, which is most of the time.
Using the calculator
Volume
Enter the measurements and the volume appears here, in cubic metres, litres and imperial gallons, along with the surface area the bucket test needs.
What your result means
The volume is a calculation from your dimensions rather than a measurement of your pool, and how close the two are depends on which shape you chose.
| Shape | The area calculation is | Which means |
|---|---|---|
| Rectangular | Exact. Length times width. | Any error comes from the depths rather than the outline. |
| Circular | Exact for a true circle. | Same. The outline is not the problem. |
| Oval | Exact for a true ellipse. | Real pools described as oval are often stadium-shaped instead, with straight sides and rounded ends, which holds more. |
| Kidney | An approximation, and the only one of the four that is. | A rule of thumb rather than geometry. Treat it as a starting point. |
That difference is not visible in the output, which is why it is written here. Four numbers that look alike do not carry alike, and a reader has no way to tell from a figure which one they are holding.
The surface area matters more than the volume for what this site does with it, because it is the number the bucket test multiplies a millimetre drop by. why the bucket test needs the surface area covers why an error there carries straight into a loss figure.
How the calculation works
Surface area times average depth, and the four shapes differ only in how the area is found.
| Shape | Surface area | Status |
|---|---|---|
| Rectangular | length × width | Exact geometry. |
| Circular | π × radius² | Exact geometry. |
| Oval | (π ÷ 4) × length × width | Exact for an ellipse. |
| Kidney | 0.45 × (width A + width B) × length | A pool industry approximation. Not geometry, and not sourced. |
Average depth is then (shallow + deep) ÷ 2, and the volume is area × average depth. Litres are cubic metres × 1,000, and imperial gallons are litres ÷ 4.54609.
The average depth step is exact only for a floor that slopes uniformly from the shallow end to the deep end. A pool with a flat shallow section that then drops away, or with a hopper in the deep end, holds less water than that average implies, so the calculated volume comes out high.
Both of those are stated because the output cannot show them. A figure in cubic metres looks equally confident whether it came from exact geometry on a rectangle or from a rule of thumb on a kidney with a hopper floor.
Assumptions and sources
Litres in a cubic metre
Exact by definition
SI definition. The litre is defined as one cubic decimetre, so one cubic metre is exactly 1,000 litres.
Litres in an imperial gallon
Exact by definition
UK legal definition. The imperial gallon is defined as exactly 4.54609 litres in United Kingdom weights and measures law.
Kidney pool shape factor
Editorial convention
Standard pool industry approximation for a kidney shape, given in the project brief section 3.5. It is an approximation of an irregular outline, not a measurement of any particular pool.
Three of the four area formulas are geometry and need no source: the area of a rectangle, a circle and an ellipse are definitions rather than findings.
The kidney factor is not. It is a pool industry approximation for an irregular outline, it was given in the specification for this site without a source, and no published origin was found for it. It ships as what it is, and this page says so rather than letting it sit in a table with three exact formulas and inherit their authority.
The unit conversions are exact and defined: 1,000 litres to a cubic metre, and exactly 4.54609 litres to an imperial gallon under UK weights and measures law.
The average depth method is an assumption about the shape of your pool floor rather than a constant, and it is the largest single source of error in the result for most real pools.
What to do next
Three things, and the second is what this calculator exists for.
- Sanity-check the figure against what the pool was sold as, if you know it. A large disagreement usually means the floor is not the shape the average depth assumed.
- Take the surface area into the bucket test. That is the number a millimetre of level drop is multiplied by, and it is the reason this page is on a leak site at all.
- If the volume matters precisely, for dosing or for a percentage loss, measure the water rather than the pool. Filling through a meter gives an exact answer for any shape and makes every assumption on this page irrelevant.
The link is direct: use this surface area in the bucket test takes the area straight from here.
Common questions
- Why does this site have a pool volume calculator at all?
- For two reasons, and neither is the volume for its own sake. The bucket test needs a surface area in square metres to turn a millimetre drop into litres, and a loss expressed as a percentage of the pool means nothing without knowing what the pool holds.
- How accurate is the answer?
- For a rectangular pool with a uniformly sloping floor, exact. For anything else, an estimate, and the two things that spoil it are an irregular outline and a floor that does not slope evenly. The calculator states which of those applies to the shape you chose.
- Is the kidney formula reliable?
- It is an approximation and this site says so rather than presenting it alongside the others as though they were equivalent. A kidney pool is irregular by definition, so no single formula fits one, and the factor used here is a pool industry rule of thumb rather than geometry. Treat it as a starting point within perhaps ten per cent, and measure the water if you need better.
- Why does average depth not work on my pool?
- Because averaging the shallow and deep ends is exact only if the floor slopes evenly from one to the other. Most UK pools do not: a flat shallow section that then drops away, or a hopper in the deep end, both hold less water than a uniform slope would. If your pool has either, the calculated volume is too high.
- How do I get the real volume?
- Measure the water going in. Fill the pool through a meter, or from empty with a known volume, and you have the answer with no geometry involved at all. That is the only method that is exact for every shape, and it is the one to use if the number really matters.
- Gallons or litres?
- Both are given, and the gallons are imperial rather than US. Almost every UK pool is described in gallons and almost none of those figures says which kind, so the two are 20 per cent apart and unlabelled.