Gallons of roof runoff from a storm or season.
Each square foot of roof yields roughly 0.6 gallons per inch of rain, discounted for splash and overflow losses. A modest roof captures more irrigation water than tanks can hold, cutting tap-water use for the driest weeks.
Rainfall Collection
Gallons = area x inches x 0.623 x efficiency
Gallons = area x inches x 0.623 x efficiency Each square foot of roof yields roughly 0.6 gallons per inch of rain, discounted for splash and overflow losses.
A modest roof captures more irrigation water than tanks can hold, cutting tap-water use for the driest weeks.
This calculator takes 3 inputs: Roof footprint, Rainfall, Collection efficiency. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.