Enter your values
The starting values are editable examples. Results update when you change your inputs.
Your result
Updates as you change your values.
How it is calculated
Collected litres = horizontal area in m² × rainfall in mm × collection percentage / 100. One millimetre over one square metre is one litre.
Worked example
100 m² with 20 mm of rain gives 2,000 L before losses. At 80 % collection, the estimated yield is 1,600 L.
Before you calculate
Use the horizontal projected area, not the sloping roof area, and rainfall measured over the same period.
Interpreting the result
The percentage combines losses. This is not a tank sizing model or a forecast of rainfall; it does not assess water quality.
Use the units shown beside each field. Monetary fields labelled EUR stay in euros; changing language does not exchange currencies. Results are estimates under the stated assumptions.