Rainwater Calculator
How much rain could your roof collect, and how far could that water go? Use local rainfall history to explore collection potential, tank sizing, and water supply through wet and dry months. Free to use.
New to rainwater harvesting? Learn the basics or explore the rainfall data.
Help us improve rainfall coverage
Our new NASA POWER rainfall dataset is being tested. Tried it in your area? Share your feedback to help us improve the calculator.
We’re seeking funding to bring higher-resolution PRISM rainfall data to every U.S. state. Contact us about supporting this work.
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Find Your Location
Enter your address or click on the map to select your property and get location-specific rainfall data.
Rainwater Site Planner
Measure your roof catchment on aerial imagery, arrange multiple tanks, and compare round, rectangular, and slimline footprints before planning an installation.
Additional tools include custom rainfall analysis for your own data and a firm-yield calculator.