Rain Barrel Sizing Calculator
Rain Barrel Sizing Calculator
Asphalt 0.9, metal 0.95, tile 0.85.
| Detail | Value |
|---|---|
| Roof Area (footprint) | 1,000 sq ft |
| Rainfall | 1.0 inches |
| Runoff Efficiency | 90% |
| Water Captured | 561 gal (2,122 L) |
| 55-Gallon Barrels Needed | 11 barrels |
| Total Weight | 4,676 lbs |
| Garden Irrigated (1 in) | 900 sq ft |
Collection Comparison (gallons)
Summary
What the Numbers Mean
With the defaults (1,000 sq ft roof, 1 inch of rain, 90% efficiency), a single storm yields 561 gallons — enough to fill eleven 55-gallon barrels, irrigate 900 sq ft of garden with an inch of water, or weigh over 4,600 lbs.
The 0.623 Factor
One inch of rain on one square foot is 1/12 of a cubic foot = 0.623 gallons. Multiply by roof footprint (pitch doesn't matter — a flat and steep roof of the same footprint catch the same vertical rainfall) and your runoff efficiency.
Frequently Asked Questions
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