This free water tank capacity calculator tells you how many litres and gallons your tank holds. Measure your tank and enter its inside dimensions. The calculator gives the full capacity and the water currently in it (from the water depth) in litres, US gallons and imperial gallons, which is what “gallons” usually means on tank labels in Pakistan and the UK. It also shows how many days the water will last your household.
How to use the Water Tank Capacity Calculator
- Choose the tank shape and your unit.
- Enter length and width, or the diameter, and the height.
- Add the current water depth if you want to see how much is left.
- Enter people in the house and litres per person per day, then press Calculate capacity.
Measure inside dimensions for the water tank capacity calculator; outside measurements overstate the volume. For the history of the imperial and US gallon, see Wikipedia’s gallon article.
Tank volume formulas
For a partly filled horizontal tank, the calculator uses the circular-segment area for the water depth, so readings are accurate at any level, not just a straight percentage.
Common tank sizes
| Tank | Litres | Imperial gallons |
|---|---|---|
| Plastic tank “500 gallon” | ≈ 2,270 | 500 |
| Plastic tank “1000 gallon” | ≈ 4,550 | 1,000 |
| Concrete 6 × 4 × 4 ft | ≈ 2,718 | ≈ 598 |
| Underground 10 × 8 × 6 ft | ≈ 13,590 | ≈ 2,990 |
Frequently asked questions
How many litres is a 1000 gallon tank?
In Pakistan and the UK, tank gallons are usually imperial gallons, so 1,000 gallons ≈ 4,546 litres. A 1,000 US gallon tank is 3,785 litres.
How do I calculate the capacity of a round water tank?
Multiply π × radius² × height using inside measurements in metres, then multiply by 1,000 for litres. A tank 1.2 m across and 1.5 m high holds π × 0.6² × 1.5 × 1000 ≈ 1,696 litres.
How many litres is 1 cubic foot?
1 cubic foot = 28.317 litres (about 6.23 imperial gallons or 7.48 US gallons).
How big should my overhead tank be?
Plan for at least one day of use: people × 100–150 litres. A family of 6 at 120 L each needs about 720 L per day, so a 500-gallon (2,270 L) tank gives about 3 days of storage.
How do I calculate water tank capacity in litres?
For a rectangular tank, multiply length × width × height in feet, then multiply by 28.32. A 6 × 4 × 4 ft tank is 96 cubic feet × 28.32 = about 2,719 litres.
What is the difference between imperial and US gallons?
An imperial gallon is 4.546 litres and a US gallon is 3.785 litres. Tank labels in Pakistan and the UK usually mean imperial gallons, so a ‘500 gallon’ tank holds about 2,273 litres, not 1,893.
How long will my tank last?
Days of supply = litres in the tank ÷ (people × litres per person per day). A 2,000-litre tank for 5 people using 100 litres each lasts about 4 days.
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Results are estimates for general information. Check critical decisions with a qualified professional.