Water Tank Volume Calculator

Work out water tank volume instantly with clear inputs, formula shown and shareable results.

About Water Tank Volume Calculator

Tank volume follows the geometry: pi r squared h for a cylinder, l x w x h for a rectangle, and four thirds pi r cubed for a sphere. One cubic metre is 1,000 litres and weighs one tonne, which is the figure that matters when siting a tank on a roof or platform.

Formula

Tank volume

cylinder = pi r^2 h; rectangular = l w h; sphere = (4/3) pi r^3; 1 m3 = 1000 L = 1 tonne

Worked example

With the default values below, Water Tank Volume Calculator returns Tank volume of 5.09. Change any input above and every figure here is recalculated in your browser.

Inputs used

Tank shapeone of Cylindrical (vertical), Rectangular, Spherical: Cylindrical (vertical)
Diameter or length: 1.8 m
Width (rectangular only): 1.2 m
Height or depth: 2 m

Results

Tank volume: 5.09 m³
Capacity: 5,089 L
Capacity: 1,120 gal
Weight when full: 5.09 t

Step by step

1Values used
2Tank volume
3Tank volume= 5.09 m³
4Capacity= 5,089 L
5Capacity= 1,120 gal
6Weight when full= 5.09 t

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does the weight matter so much?

A modest 2,000 litre loft tank weighs two tonnes when full. That load must be spread across joists or it will fail the ceiling structure.

Should I allow for freeboard?

Yes. Working capacity is usually 90-95% of geometric volume to leave room for the inlet, overflow and any float valve mechanism.