Water Tank Calculator
Home & ConstructionWork out how many litres a tank holds and how long that lasts your household.
Runs entirely in your browser — nothing is uploaded
Features
- Capacity in litres, cubic metres and gallons.
- Rectangular and cylindrical tanks.
- Days of supply for your household size.
- Usable capacity, not just the theoretical volume.
- Runs in your browser.
How to use the Water Tank Calculator
- 1Choose the tank shape and enter its dimensions.
- 2Enter how many people the tank serves.
- 3Read the capacity and how many days it lasts.
Frequently asked questions
What size water tank does a family need?
The Indian norm is 135 litres per person per day for all uses, so a family of four needs about 540 litres a day. A 1,000 litre tank gives under two days of buffer — most homes size for two to three days where supply is intermittent.
How many litres is a 4 × 3 × 3 foot tank?
Thirty-six cubic feet, which is about 1,019 litres. One cubic foot is 28.32 litres, and one cubic metre is exactly 1,000.
Why is the usable capacity less than the tank size?
The outlet sits above the floor of the tank and the inlet cuts off below the top, so you never get the full volume. Around 90% is realistic, and the sediment at the bottom is not water you want anyway.