A surprising amount of water falls on even a modest roof during a rainstorm, and this calculator shows exactly how much. It is the essential first step for planning rainwater harvesting, sizing gutters and downpipes, estimating stormwater runoff, or simply appreciating how far an inch of rain goes. The math is straightforward: the volume equals the catchment area multiplied by the rainfall depth, but keeping the units consistent is where mistakes happen, so this tool handles the conversions for you. Enter the rainfall depth in millimeters or inches, the catchment area in square meters or square feet, and an optional collection efficiency to account for splash and evaporation losses, and read the harvestable volume in liters and US gallons. It is ideal for gardeners, homesteaders and anyone building a rain barrel or cistern. All computation runs locally in your browser for instant, private results.
A surprising amount of water falls on even a modest roof during a rainstorm, and this calculator shows exactly how much. It is the essential first step for planning rainwater harvesting, sizing gutters and downpipes, estimating stormwater runoff, or simply appreciating how far an inch of rain goes.
Yes. Rainfall Volume Calculator is completely free, with no sign-up and no usage limits.
Yes. Rainfall Volume Calculator runs in any modern web browser. There is nothing to download or install.
Yes. Rainfall Volume Calculator runs entirely on your device in your browser, so nothing you enter is uploaded to a server.