Water Tank Capacity Calculator
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Updated
Enter the tank size and get the capacity in litres — and how many people it serves at 135 litres per person per day. Works for rectangular (sump/RCC) and cylindrical (Sintex-type) tanks.
Water Tank Capacity Calculator
Litres from the tank size (1 m³ = 1000 L) · demand 135 L/person/day (IS 1172)
Rectangular tank
2,000 litres · 2 m³
Measure the internal size. A family of 5 needs ~675 L/day (135 L each); a day's storage plus a margin is common.
Tank capacity
2,000 litres
2 m³ · serves about 15 people for a day at 135 L each
Litres
2,000
Volume (m³)
2
People / day
15
Family of 5
3 days
Common capacities
500 L
4 people
0.50 m³
1,000 L
7 people
1 m³
2,000 L
15 people
2 m³
5,000 L
37 people
5 m³
135 litres per person per day is the IS 1172 figure for a domestic supply with flushing. Size overhead storage for at least a day, and remember the usable depth is a little less than the tank height once you allow for the outlet and air gap.
How it works
- Volume = length × width × height (rectangular), or π × (diameter/2)² × height (cylindrical).
- Litres = volume in m³ × 1,000 (1 m³ = 1,000 litres).
- People served = litres ÷ 135 (the IS 1172 domestic demand per person per day).
Worked example
- A 2 × 1 × 1 m tank holds 2 m³ = 2,000 litres — about 15 people for a day at 135 L each.
- A cylindrical tank 1 m across and 1.5 m tall holds π × 0.5² × 1.5 = 1.178 m³ = 1,178 litres.
Sizing guide
| Household | Daily need | Suggested storage |
|---|---|---|
| 3 people | 405 L | 500–1,000 L |
| 5 people | 675 L | 1,000–1,500 L |
| 8 people | 1,080 L | 2,000 L |
Store at least a day's supply; two days is safer where the municipal supply is intermittent.
Frequently asked questions
How do I calculate water tank capacity in litres? Work out the volume in cubic metres (L × W × H, or π × r² × H) and multiply by 1,000. A 2 × 1 × 1 m tank is 2 m³ = 2,000 litres.
What is the water requirement per person per day? IS 1172 takes 135 litres per person per day for a domestic supply with flushing, so a family of five needs about 675 litres a day.
How big a tank for a family of 5? Around 1,000 litres for a day's storage, or 1,500 L for a comfortable margin — a 1.2 × 0.9 × 1 m tank is close to 1,000 L.
Is the full tank height usable? Not quite — the outlet sits above the floor and there's an air gap at the top, so usable capacity is a little less than the size calculated.
Related
CivilSite Editorial Team✓ Engineer reviewed
Written and reviewed by practising civil engineers with 10+ years of Indian residential construction experience.