Rainwater harvest

Roof area times rainfall times runoff coefficient gives the liters you can actually collect.

Calculated in this browser. Nothing is sent anywhere.

Volume = area × rain × efficiency; first-flush diversion and tank size are not modeled. Area 1–100000 m², rain 0.1–5000 mm.

How to use

  1. Enter the roof's plan area.
  2. Enter rainfall and a runoff coefficient.
  3. Read liters and gallons.

What it supports

Area 1–100,000 m², rainfall 0.1–5,000 mm, collection efficiency 1–100% (presets: metal 90%, asphalt 85%, tile/concrete 80%; first-flush losses not included). Area is the roof's plan footprint, not the slope.

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