See how much rainwater your roof can capture so you can size a rain barrel or cistern for the garden. Enter the footprint of the roof area that drains to your downspout in square feet and the rainfall in inches, and the calculator estimates the gallons collected using the rule that one inch of rain on one square foot yields about 0.623 gallons. It applies a collection efficiency factor, since some water is lost to splash, first flush and evaporation, typically leaving eighty to ninety percent usable. Enter your barrel size and it shows how many barrels that storm would fill. Even a modest roof and a light rain can fill a barrel fast, which is why overflow routing matters. All math runs locally in your browser with no signup.
See how much rainwater your roof can capture so you can size a rain barrel or cistern for the garden. Enter the footprint of the roof area that drains to your downspout in square feet and the rainfall in inches, and the calculator estimates the gallons collected using the rule that one inch of rain on one square foot yields about 0.
Yes. Rain Barrel Capacity Calculator is completely free, with no sign-up and no usage limits.
Yes. Rain Barrel Capacity Calculator runs in any modern web browser. There is nothing to download or install.
Yes. Rain Barrel Capacity Calculator runs entirely on your device in your browser, so nothing you enter is uploaded to a server.