Rainfall Volume Calculator
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.
How to use Rainfall Volume Calculator
- Enter the rainfall depth.
- Enter the roof or catchment area.
- Read the collected volume in liters.
- Read the equivalent in gallons.
Frequently asked questions
How does it convert rainfall to water volume?
It multiplies the rainfall depth by the catchment area, so one millimeter of rain over one square meter yields one liter of water.
What area should I enter for a roof?
Use the flat footprint area of the roof, its length times width as seen from above, since rainfall depth applies to the horizontal projected area.
Does it show both metric and US units?
Yes, it reports the collected volume in liters and gallons so you can plan a rain barrel or tank in whichever unit you use.
What is Rainfall Volume Calculator?
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.
Is Rainfall Volume Calculator free to use?
Yes. Rainfall Volume Calculator is completely free, with no sign-up and no usage limits.
Does Rainfall Volume Calculator work in a web browser?
Yes. Rainfall Volume Calculator runs in any modern web browser. There is nothing to download or install.
Is my data private with Rainfall Volume Calculator?
Yes. Rainfall Volume Calculator runs entirely on your device in your browser, so nothing you enter is uploaded to a server.
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