Work out how much a tank holds. Choose a cylindrical or rectangular shape, enter the dimensions in metres, and the calculator gives the full volume in litres, cubic metres and both US and UK gallons. Useful for water tanks, fuel tanks, aquariums and pools; it all runs in your browser.
Enter all dimensions in metres.
Enter the dimensions to find the volume.
How it works
For a rectangular tank the volume is length × width × height. For a cylinder it is π × radius² × height, and since you usually measure across the top, the tool takes the diameter and halves it for you. Enter every dimension in metres.
One cubic metre is exactly 1000 litres, so the tool multiplies the m³ result by 1000 for litres, then divides by 3.785 for US gallons and 4.546 for UK gallons. These are two genuinely different units — a US gallon is about 20% smaller than a UK one, so the tool shows both.
The result is the total (full) capacity, ignoring wall thickness, inlets and any dip below the outlet. For a partially filled tank, use the height of the liquid rather than the tank; for a horizontal cylinder filled part-way, the shape of the wetted area is more complex and not covered here.
Practical examples
A cylindrical water tank
A tank 2 m across and 1 m tall: enter diameter 2 and height 1. The volume is about 3.14 m³, or roughly 3,142 litres — around 830 US gallons.
A rectangular aquarium
A tank 1.2 m long, 0.5 m wide and 0.6 m tall holds 0.36 m³ = 360 litres. Fill it to 0.55 m instead of the full 0.6 m and enter that height to get the actual water volume.
A fuel or rainwater butt
Enter the internal dimensions of a rectangular container — say 1 × 1 × 1 m — to confirm it is a 1,000-litre (1 m³) IBC before ordering a pump or fittings to match.
Frequently asked questions
What units should I enter?
Metres for every dimension. If you measured in centimetres, divide by 100 first (150 cm = 1.5 m). The volume then comes out in cubic metres and litres automatically.
How do I convert cubic metres to litres?
Multiply by 1000 — one cubic metre is exactly 1000 litres. The tool does this for you, so a 2.5 m³ tank shows as 2,500 litres.
Why are the US and UK gallon figures different?
They are different units. A US gallon is about 3.785 litres and a UK (imperial) gallon is about 4.546 litres — roughly 20% larger. Always check which gallon a spec refers to; the tool shows both to avoid mix-ups.
Do I enter the radius or the diameter for a cylinder?
The diameter — the full width across the top, which is what you normally measure. The tool halves it to get the radius for the π r² h formula.
Can I calculate a partially filled tank?
For a vertical tank, yes: enter the height of the liquid instead of the tank’s full height and you get the current volume. A horizontal cylinder filled part-way needs a more complex partial-area formula that this tool does not include.
Does it account for wall thickness?
No. It uses the dimensions you enter as the internal space. For an accurate capacity, measure the inside of the tank; measuring the outside slightly overstates the volume by the wall thickness.
Can I use it for a swimming pool?
For a simple rectangular pool of constant depth, yes. Pools with a sloping floor or curved ends are not a single box or cylinder, so you would split them into sections or use an average depth.
What about oval, capsule or cone-bottom tanks?
Those shapes need their own formulas and are not covered here. This tool handles the two most common cases — upright cylinders and rectangular boxes.
Is anything I enter uploaded?
No. The calculation is done entirely in your browser and nothing is sent to a server or stored.
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