Home Improvement & DIY
Rainwater Harvesting Calculator
Lets users estimate and size rainwater harvesting instantly with formula, steps and examples — no manual math.
Enter your details
m²
mm
0.30.95
Your result
Annual harvest
80,000 litres
Harvestable water = area × rainfall × runoff = 80,000 litres/year.
In kilolitres
80 kL
About this calculator
Rainwater harvest potential (litres) = roof area (m²) × rainfall (mm) × runoff coefficient. 1 mm of rain on 1 m² ≈ 1 litre; the coefficient accounts for losses.
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