Free Rain Barrel Calculator
Estimate how much rainwater you can collect from your roof based on roof area and local rainfall.
sq ft
in
%
Gallons Collected
748 gal
Standard Barrels Needed (55 gal)14
Liters Collected2,830 L
Gallons Collected vs Roof Catchment Area
How Rain Collection Is Calculated
One inch of rain on 1 square foot of roof produces about 0.623 gallons of water.
Formula
Gallons = Roof Area (sq ft) x Rainfall (in) x 0.623 x Efficiency
Efficiency accounts for losses from gutters, splashing, and first-flush diverters.
Example Calculation
1,500 sq ft roof, 1 inch of rain, 80% collection efficiency.
- 01Raw collection = 1,500 x 1 x 0.623 = 934.5 gallons
- 02With 80% efficiency = 934.5 x 0.80 = 747.6 gallons
- 03Standard barrels = ceil(748 / 55) = 14 barrels
Frequently Asked Questions
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