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Fish Tank Volume Calculator

Fish Tank Volume Calculator UK

Volume

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Enter your tank dimensions to see the volume.

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A fish tank volume calculator for the UK, showing results in litres and UK (imperial) gallons. Enter your dimensions and read the capacity instantly.

UK gallons and litres

In the UK, aquariums are usually measured in litres, but tanks are sometimes still listed in imperial gallons. One UK gallon equals 4.546 litres, which is larger than a US gallon.

Common tank sizes and their volume

Dimensions (cm)UK gallonsUS gallonsLitres
30 × 30 × 305.97.127
40 × 25 × 255.56.625
45 × 30 × 308.910.741
60 × 30 × 3011.914.354
60 × 30 × 3614.317.165
80 × 35 × 4024.629.6112
100 × 40 × 504452.8200
120 × 40 × 5052.863.4240
120 × 50 × 506679.3300
150 × 50 × 6099118.9450

Calculated with the same formula as the calculator above. Values are rounded.

How to calculate fish tank volume in the UK

Most tanks sold in the UK are listed in centimetres and litres, but older tanks, second-hand listings and some product labels still use imperial gallons. This calculator shows both.

  1. Measure the length, width and height in centimetres.
  2. Multiply them and divide by 1,000 for litres. For example, 80 x 35 x 40 cm = 112,000 cm³ = 112 litres.
  3. Divide the litres by 4.546 for UK gallons. 112 / 4.546 = 24.6 UK gallons.

Or pick your shape above, enter the measurements and read litres and UK gallons straight away.

UK gallons are not US gallons

Litres
1 UK (imperial) gallon4.546
1 US gallon3.785

A UK gallon is about 20 percent bigger. That matters because many online guides, forums and product labels come from the US. If a treatment says “5 ml per 10 gallons” and it means US gallons, counting your tank in UK gallons gives the fish about 17 percent less medicine than intended. Check which gallon the label means, or dose by litres when you can.

The same tank gives two different gallon numbers. A 100 litre tank is 22.0 UK gallons but 26.4 US gallons.

Before you use the size table

The table of common sizes above uses outside dimensions, which is how UK shops list their tanks. The water in a set-up tank is lower, often by 10 to 15 percent once you allow for the glass, gravel and the gap at the top. Use the water volume calculator for the real figure when you dose treatments.

Old tanks measured in feet and inches

Older UK tanks are often described in feet, such as a “3 foot tank” or a “4 x 1.5 x 1.5”. Use feet as the unit in the calculator, or convert: a 4 x 1.5 x 1.5 foot tank is 9 cubic feet, which is about 254.9 litres or 56.1 UK gallons. The calculator in feet has more examples.

Converting UK gallons to litres

Multiply UK gallons by 4.546:

  • 10 UK gallons = 45.5 litres
  • 20 UK gallons = 90.9 litres
  • 30 UK gallons = 136.4 litres
  • 50 UK gallons = 227.3 litres

For US gallon conversions, use the gallon calculator. For metric results only, use the litres calculator.

Volume at a glance

Drag to fill a 60 by 30 by 30 cm (54 L) tank and watch the volume change.

50% full = 27 L

Formula

V = length × width × height

Related calculators

In Litres In Gallons Tank Weight Tank Size Substrate

Frequently asked questions

How do I calculate fish tank volume in the UK?
Measure in centimetres, multiply length by width by height, and divide by 1000 for litres. The result also shows UK gallons.
What is a UK gallon in litres?
One UK (imperial) gallon equals 4.546 litres, compared with 3.785 litres for a US gallon.
How many UK gallons is a 100 litre tank?
About 22 UK gallons (100 divided by 4.546).
Why does the UK use litres for tanks?
The UK uses the metric system for most measurements, so aquarium volumes are normally quoted in litres.

Related guides

Learn the core ideas behind fish tank volume before or after using the calculator.