Rainwater Harvesting Calculator

Units
sq ft

Measure the footprint, not the sloped surface.

in

One storm, or an annual total (Michigan averages roughly 32–36 in).

%

Losses to splash, evaporation and first-flush diverters. 75–90% for metal or shingle roofs.

gal

Rainwater collected

748 gal

55 gal barrels to hold it all
14 barrels
Liters
2,832 L
Gallons per inch of rain
748 gal
Theoretical maximum (100%)
935 gal
Water weight
6,239 lb

80% collection efficiency applied. Check local rules on rainwater collection and use.

Open the full rainwater harvesting calculator with the formula and FAQs at Calcs for Life