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Water Tank Capacity Calculator

Work out how much water a rectangular or round tank holds, in litres, imperial and US gallons, from its inside measurements in feet, metres, inches or cm.

Rules last checked 25 October 2026Every step shown

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Capacity

2,718 litres

In imperial gallons
598 gallons
In US gallons
718 gallons
In cubic metres
2.718 m³
In cubic feet
96 ft³
Water at 100% full
2,718 litres (about 2,718 kg)

The tank holds about 2,718 litres (598 imperial gallons) when full.

How it's worked out

  1. Volume6 × 4 × 4 ft2.7184 m³
  2. Litres2.7184 m³ × 1,0002,718
  • Use inside measurements; walls and the gap below the overflow reduce what a tank really holds. A litre of water weighs about 1 kg, so check the roof or stand can take the full weight.

The formulas

Rectangular: length × width × height · Round: π × (diameter ÷ 2)² × height

1 ft³ = 28.3168 litres · 1 m³ = 1,000 litres · 1 imperial gallon = 4.546 litres · 1 US gallon = 3.785 litres

Example

An overhead tank 6 ft long, 4 ft wide and 4 ft deep holds 96 ft³: 2,718 litres, 598 imperial gallons or 718 US gallons.

Questions people ask

How many litres is a 6 × 4 × 4 ft tank?

96 cubic feet, which is about 2,718 litres or 598 imperial gallons.

How do I work out a round tank's capacity?

π × radius² × height. A tank 1.2 m across and 1.5 m high holds about 1,696 litres.

How many litres are in a cubic foot?

28.32 litres. A cubic metre is 1,000 litres.

How heavy is a full tank?

A litre of water weighs about 1 kg, so 2,718 litres weighs about 2.7 tonnes plus the tank. Make sure the roof or stand can carry it.

Formula and rules last checked 25 October 2026Written and tested by the CalculatorDex teamReport a problem