basic

Rainwater Barrel Fill Time from Roof Area Calculator

fill_time_h = barrel_gal / (roof_sqft · rainfall_in_per_h · 0.623 · efficiency).

Estimate how long it takes to fill a rainwater collection barrel from a sloped roof at a given rainfall rate. 1 inch of rain on 1 ft² yields ~0.623 gallons; multiply by roof footprint and rainfall rate, then divide barrel size to get hours. Default 90 % collection efficiency accounts for splash and overflow.

Marcus Laurent By Marcus Laurent
Published Last reviewed 1 min read

Inputs

ft²
in/h
gal
%

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/h = sqft · in/h · 0.623 · efficiency; fill_h = barrel_gal / (gal/h).

In depth

Estimate how long it takes to fill a rainwater collection barrel from a sloped roof at a given rainfall rate. 1 inch of rain on 1 ft² yields ~0.623 gallons; multiply by roof footprint and rainfall rate, then divide barrel size to get hours. Default 90 % collection efficiency accounts for splash and overflow.