Pool volume in litres, gallons and cubic metres
A pool described as 10,000 imperial gallons holds 45,461 litres, or about 45.5 cubic metres. Those gallons are imperial, because a UK pool figure almost always is, and it almost never says so.
Last reviewed 14 August 2026
The short answer
Two exact conversions, and one question to settle before using either.
| Imperial gallons | Litres | Cubic metres |
|---|---|---|
| 1,000 | 4,546 | 4.5 |
| 5,000 | 22,730 | 22.7 |
| 10,000 | 45,461 | 45.5 |
| 15,000 | 68,191 | 68.2 |
| 20,000 | 90,922 | 90.9 |
Every row is exact arithmetic on two defined conversions. The question to settle first is whether your gallons figure is imperial or US, because that decision moves the answer by about a fifth and nothing in the number itself tells you.
How this works in practice
Three units, three audiences, and each one wants a different answer to the same question.
- Imperial gallons. What a UK pool installer, a UK pool forum and most UK chemical dosing instructions use. Multiply litres by 4.54609 to go the other way.
- Litres. What a leak is felt in, and what a millimetre of level drop over a square metre gives you directly.
- Cubic metres. What a UK water bill charges in, so a pool loss in cubic metres per year is comparable with a bill without further conversion.
The site reports all three for that reason rather than picking one. converting litres to cubic metres covers the imperial against US question in more detail, because it is the one that actually costs people accuracy.
What changes the answer
Three things, and only the first is about the conversion itself.
- Which gallon. About a fifth, in whichever direction the mistake goes, and unlabelled figures are the norm.
- Whether the figure is nominal or measured. A pool sold as 10,000 gallons holds what its dimensions and water level give it, which is a different number.
- The water level. A pool run a few centimetres below its normal line holds meaningfully less, and on a large surface area a small drop is a large volume.
For a leak calculation none of this matters much, because the bucket test works from surface area and a level drop rather than from the total volume. The volume matters for dosing and for expressing a loss as a percentage.
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.
Both conversions are exact and defined rather than measured: one thousand litres to a cubic metre by the definition of the litre, and exactly 4.54609 litres to an imperial gallon under UK weights and measures law.
The pool sizes in the table are round imperial figures converted exactly. They are not measurements of any particular pool and are there to make the scale readable.
What to do next
Two things.
- Settle whether your gallons figure is imperial or US before converting. In the UK, assume imperial unless the source is American.
- If the volume matters precisely, calculate it from your own dimensions rather than trusting the nominal figure, or measure the water going in.
And for a leak, take the surface area rather than the volume. use this surface area in the bucket test is what the area is for.
Common questions
- How do I convert my pool from gallons to litres?
- Multiply by 4.54609 for imperial gallons. Four and a half is close enough for a sanity check and is about one per cent light.
- Why does the site want cubic metres?
- Because that is the unit a UK water bill charges in, so a pool loss expressed in cubic metres can be compared directly against a bill without any further conversion.
- Is the volume my pool was sold as the volume it holds?
- Not necessarily. A nominal capacity describes a model rather than an installation, and the water it actually holds depends on the floor shape and the water level. If the number matters, calculate it from your own dimensions or measure the fill.
- Which gallon is my figure in?
- Imperial, if it came from a UK source. The US gallon is about 3.785 litres against the imperial 4.54609, a difference of about 20 per cent, which on a pool is thousands of litres.