Rainfall & harvesting
Rainwater harvesting calculator
Estimate annual yield from a roof and size a storage tank against your intended use.
Result
Annual yield
36,720litres/year
In cubic metres
36.7m³/year
Share of your demand met
100%
Suggested tank size
1,800litres
Approximately 18 days of the lesser of supply or demand — a common UK sizing rule of thumb.
Average daily yield
101litres/day
Highly seasonal. A tank sized on averages can still run dry in a dry summer.
Method
Annual yield = roof plan area × annual rainfall × runoff coefficient × filter efficiency. Tank sizing uses a simple demand-and-supply rule of thumb against the shorter of a supply-limited or demand-limited estimate.