Water Tank Capacity Calculator in Litres
Pick a rectangular or round tank and enter its inside size. You get capacity in litres, m³ and cft, and how many days it lasts at your daily use.
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Tank capacity
3,600L
- Volume
- 3.6 m³
- Volume
- 127.1 cft
- Lasts about
- 6.7 days
Usable water is a little less: the top 100–150 mm above the overflow stays empty.
Show working
- 2 × 1.5 × 1.2 = 3.6 m³
- 3.6 × 1000 = 3,600 L
- 3,600 ÷ (4 × 135) = 6.7
How to use
- Choose rectangular or round (cylindrical) tank.
- Enter the inside length, width or diameter, and water depth.
- Enter people and litres per person to see how long it lasts.
Good to know
Rectangular: litres = length × width × height (m) × 1000. Round: litres = π × (diameter ÷ 2)² × height × 1000. In feet, 1 cubic foot = 28.32 litres. Use inside measurements and the water depth, not the outer height.
Leave freeboard: the top 100–150 mm of an overhead or sump tank does not fill because of the overflow pipe, so usable capacity is a little less than the full box.
Daily use: IS 1172 recommends 135 litres per person per day for homes in cities with full flushing; many families use less. For 4 people that is 540 litres a day, so a 1,000 litre tank lasts under 2 days.
Questions
How many litres in a 10 × 5 × 4 ft tank?
200 cft × 28.32 = 5,663 litres.
How to calculate litres of a round tank?
π × radius² × height in metres × 1000. A 1.2 m wide, 1.2 m deep tank holds about 1,357 L.
How much water does a family need per day?
IS 1172 suggests 135 litres per person per day for city homes; 4 people need about 540 L.
Should I use inside or outside size?
Inside size and water depth. Wall thickness and the empty space above the overflow do not hold water.
What size tank for 4 people?
For one day of storage about 500–600 L; most homes keep 1,000–2,000 L overhead plus a sump.