Work out water tank sizing for building instantly with clear inputs, formula shown and shareable results.
Storage is sized on daily demand, commonly 135 litres per person per day for residential use, multiplied by the days of autonomy required, plus a fire reserve where the code demands one. A cubic metre is a thousand litres, so the conversion to physical tank size is direct.
Storage
Litres = occupants x litres per person per day x storage days x (1 + fire reserve)
Litres = occupants x litres per person per day x storage days x (1 + fire reserve). Storage is sized on daily demand, commonly 135 litres per person per day for residential use, multiplied by the days of autonomy required, plus a fire reserve where the code demands one.
Usually yes. The underground sump holds the bulk and the overhead tank holds enough for a few hours, which limits the structural load at roof level and the residence time of stored water.
This calculator takes 4 inputs: Building occupants, Water demand per person per day, Days of storage, Fire reserve addition. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.