Rain Barrel Capacity Calculator
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.
How to use Rain Barrel Capacity Calculator
- Enter the roof catchment area draining to the barrel.
- Enter the rainfall depth in inches.
- Read the gallons a storm collects.
- Enter your barrel size to see how many barrels you need.
Frequently asked questions
How much water can a roof collect?
It multiplies your roof catchment area by the rainfall depth, since roughly 0.62 gallons fall on each square foot per inch of rain, to give the gallons captured.
Does the full roof area count?
Only the footprint that drains to your barrel counts, so use the horizontal plan area feeding that downspout rather than the sloped roof surface.
How does it work out barrels needed?
It divides the collected gallons by your barrel capacity to show how many barrels it takes to store a given storm's runoff.
What is Rain Barrel Capacity Calculator?
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.
Is Rain Barrel Capacity Calculator free to use?
Yes. Rain Barrel Capacity Calculator is completely free, with no sign-up and no usage limits.
Does Rain Barrel Capacity Calculator work in a web browser?
Yes. Rain Barrel Capacity Calculator runs in any modern web browser. There is nothing to download or install.
Is my data private with Rain Barrel Capacity Calculator?
Yes. Rain Barrel Capacity Calculator runs entirely on your device in your browser, so nothing you enter is uploaded to a server.
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