How Much Rainwater a Roof Collects
Collected water (L) = roof area (m2) x rainfall (mm), since 1 mm over 1 m2 is 1 L. A 50 m2 roof in a 50 mm downpour catches 50 x 50 = 2500 L.
Open the interactive Everyday Lifestyle tool →Formula: L = area m2 x rainfall mm
Key facts
| Formula | L = area m2 x rainfall mm |
|---|---|
| 1 mm over 1 m2 | 1 L |
| 50 m2 roof, 50 mm | 2500 L |
| 100 m2 roof, 10 mm | 1000 L |
Frequently asked questions
How much rain does a 50 m2 roof collect in a 50 mm storm?
2500 L: 50 m2 x 50 mm, since 1 mm per m2 equals 1 liter.
Why does 1 mm equal 1 liter per square meter?
1 mm depth over 1 m2 is 0.001 m x 1 m2 = 0.001 m3 = 1 L.
Is all of it usable?
No. Real systems lose some to splash, first-flush diversion, and overflow.
Related pages
Rain Roof Water Collection is part of Everyday Lifestyle on GOAT Lab — a free reference you can use without signing up, and it works offline. Open the tool above for any custom value.
Part of GOAT Lab — 26 free, browser-based science, engineering and developer tools. No sign-up.