Rain Barrel Capture
Calculator
Results
- Captured
- 1,020
Home and garden results
| Captured | 1,020 |
formula-map diagram
- Captured
- 1,020
Home and garden relationship
Formula
V = A × mm × e= 1020
Note
This result uses the values you entered and a simplified planning equation; verify quantities and local requirements before purchasing or building.
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See all →Frequently asked questions
How much rainwater can I actually collect from my roof?+
Multiply your roof's footprint area by the rainfall depth and a runoff efficiency factor (typically 80-90%, since some water evaporates or is absorbed by roofing material) to estimate gallons or liters captured per storm.
Why isn't 100% of the rain that falls on my roof collected?+
Some water evaporates before reaching the gutter, some is absorbed by roofing materials like shingles, and splashing or overflow during heavy downpours loses more, which is why realistic runoff coefficients sit around 0.8-0.9 rather than 1.0.
Does roof shape or slope affect how much water I can capture?+
The calculation uses the horizontal footprint area, not the sloped surface area, since that's what determines how much rain actually falls onto the roof from directly above. A steeper roof doesn't collect more water than a flatter one of the same footprint.
How many barrels do I need for a typical rainstorm?+
A single inch of rain on just 100 square feet of roof produces about 62 gallons, which quickly exceeds a standard 55-gallon barrel — this is why many setups link multiple barrels together or include an overflow diverter back to a garden bed or drain.
Is collected rainwater safe to use on vegetable gardens?+
Rainwater is generally safe for watering edible plants when your roofing material doesn't contain lead flashing or certain treated wood, but it's best applied to soil rather than directly on edible leaves, and isn't recommended as drinking water without treatment.