basic

Rain-Barrel Collection Volume Calculator

Gal = roof_sqft · rainfall_in / 12 · 7.481 · efficiency.

Estimate the gallons of rainwater collected from a roof during a storm: gallons = roof_area_sqft × rainfall_in × 0.6234 × efficiency. The 0.6234 = 7.481 gal/cu-ft ÷ 12 in/ft. Default 90 % efficiency accounts for splash and gutter losses.

Marcus Laurent By Marcus Laurent
Published Last reviewed 1 min read

Inputs

sq ft
in
%

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

Gal = roof_sqft · rainfall_in · 0.6234 · efficiency

In depth

Estimate the gallons of rainwater collected from a roof during a storm: gallons = roof_area_sqft × rainfall_in × 0.6234 × efficiency. The 0.6234 = 7.481 gal/cu-ft ÷ 12 in/ft. Default 90 % efficiency accounts for splash and gutter losses.