Rainwater Collection Calculator โ Estimate Roof Runoff and Tank Capacity
Use roof area, expected rainfall and collection efficiency to estimate collectable water and the number of tanks needed.
Collectable water
Estimated loss
Tanks needed
One millimetre of rain on 1 mยฒ of horizontal area equals 1 litre in theory. For a pitched roof, use its footprint rather than sloped surface area. Adjust efficiency for gutter leaks, first-flush diversion and evaporation; existing water and overflow are not included.