About the Water Tank Volume Calculator
Tank capacity is straightforward geometry, but the useful number is usually the volume at a partial fill. This calculator gives the full capacity of rectangular, vertical and horizontal cylindrical tanks, plus the volume at the current level so you know exactly how much water you have.
Also known as: tank capacity calculator, water storage volume, how many litres in a tank, tank size calculator, cistern volume.
How to use this calculator
- Enter tank shape, current water level and the other fields.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
Rectangular V = l × w × h · Cylinder V = πr²h · 1 m³ = 1,000 litres
Worked example
Using the values pre-filled in the calculator above:
- Tank shape: Rectangular
- Length = 2 m
- Width = 1 m
- Height = 1.2 m
- Current water level = 0.8 m
the calculator returns:
- Full capacity: 2,400 litres
- In cubic metres: 2.4
- In US gallons: 634.01
- In imperial gallons: 527.93