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05

Size storage from the roof

Rainwater capture calculator

Translate roof area and a design storm into collectable gallons or liters with a user-set efficiency factor.

Live worksheet

Enter your measurements

Roof footprint, not roof slope

Collectable water estimate

265US gallons
Liters1,003
55-gal barrels5
200-L tanks6

Plan screened inlets, a stable full-tank base, and overflow away from foundations. Check local rules before installation or edible-garden use.

Read before you buy

Why one inch of rain overwhelms a small barrel

Roof area turns modest rainfall into surprising volume. Storage, overflow, and safe use must be planned together.

Read the guide

Sources & further reading

  1. Harvesting rainwater for use in the gardenOregon State University Extension
  2. Rain barrels in the home gardenPenn State Extension