Calculators / Garden and water

Rainwater harvest calculator

Use the roof area seen from above, not the sloped surface. Swiss lowlands get about 1000 mm of rain a year.

m²
mm
Per year80,000L
Per month (average)6,667L

How it is calculated

Litres = roof area × rainfall in mm × run-off coefficient (1 mm on 1 m² = 1 litre). Coefficients: tiles and metal 0.8–0.9, flat gravel roof 0.5–0.6, green roof 0.3.

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