Rain barrel and rainwater harvesting calculator
How much rainwater your roof can collect per storm and per year, how fast a rain barrel fills, and how many barrels make sense.
Roofs collect a surprising amount of water: an inch of rain on 1,000 ft² of roof is about 600 gallons. This works out what your roof collects and how that compares with a rain barrel.
Making the most of it
- Barrels fill fast and empty slowly. Use the water between storms so there’s room for the next one.
- A soaker hose or drip line works on barrel pressure if the barrel is raised on blocks; sprinklers don’t.
- For larger volumes, directing downspouts into planted areas or a rain garden stores water in the soil itself, often more of it than barrels hold, and is allowed almost everywhere.