Water Tank Capacity Calculator
Litres in a sump, overhead tank or drum — from simple measurements.
How much water fits?
Enter the inside measurements of your tank.
How to use this tool
Measure the inside of the tank (not the outside walls). For a sump, height means the depth up to the overflow pipe.
Good to know
1 cubic foot = 28.32 litres and 1 cubic metre = 1,000 litres. Add the current water depth to see how full the tank is.
Step by step
- Choose the tank shape and the unit you measured in.
- Enter the inside length, width and height — or the diameter for a round tank.
- Optionally enter the current water depth.
- Tap Calculate capacity to see litres, kilolitres, cubic feet and gallons.
Tank volume formulas
| Shape | Volume | Then convert |
|---|---|---|
| Rectangular / sump | length × width × height | ft³ × 28.32 = litres |
| Round, standing | π × (diameter ÷ 2)² × height | m³ × 1,000 = litres |
| Round, lying down | π × (diameter ÷ 2)² × length | in³ × 0.01639 = litres |
Examples
- Sump 6 ft × 4 ft × 4 ft = 96 cu ft × 28.32 = 2,718 litres.
- Round tank 4 ft wide and 5 ft tall = 3.1416 × 2² × 5 = 62.83 cu ft = 1,779 litres.
- Underground tank 2.5 m × 2 m × 1.5 m = 7.5 m³ = 7,500 litres.
- Drum 60 cm across and 90 cm tall = 3.1416 × 30² × 90 = 254,469 cm³ = 254 litres.
How much tank do you need?
A common planning figure for Indian homes is about 135 litres per person per day (the norm used for city water supply). A family of four uses roughly 540 litres a day, so a 1,000-litre overhead tank lasts about two days, and a sump of 2,000–3,000 litres gives a comfortable buffer when supply is irregular.
Measuring tips
- Use inside dimensions; wall thickness can reduce capacity by 10% or more on cement tanks.
- Stop the height at the overflow pipe — water above it drains away.
- Moulded tanks are sold by nominal capacity (500, 1,000, 2,000 L); their tapered shape means measured volume may differ slightly.
Need other conversions? See the CFT calculator and litre to ml converter.
Frequently asked questions
How do I calculate tank capacity in litres?
Multiply length × width × height in feet to get cubic feet, then multiply by 28.32. In metres, multiply by 1,000.
How many litres is a 10 × 10 × 10 ft sump?
1,000 cubic feet × 28.32 = 28,317 litres (about 28 kilolitres).
How do I find the volume of a round tank?
π × radius² × height. Radius is half the diameter. Use the round tank option and enter the diameter.
Can it tell how much water is left?
Yes — enter the current water depth to see litres now and the percentage full, including for horizontal tanks.