How the result is calculated
Captured gallons = roof area × rainfall inches × 0.623 × collection efficiency.
SproutScale preserves full precision while calculating and rounds only the displayed result or the final purchasable unit.
ROOF CATCHMENT YIELD
Rainwater Harvesting Calculator
See the usable rainwater potential of a roof catchment for one storm or a monthly rainfall total.
FREE TOOLLocal
calculationNo garden data uploaded
calculationNo garden data uploaded
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Updates liveEnter your measurements
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Planning result
Usable capture529.55 gal
Liters2,004.56 L
Theoretical runoff623 gal
System loss93.45 gal
Use this as a planning estimate. Verify product labels, local conditions and supplier packaging before buying or applying materials.
Before you act
- Use the roof's horizontal footprint, not sloped surface area.
- Account for first-flush diversion and overflow.
- Use covered, screened storage and follow local rules.
Rainwater harvest FAQ
How much rain comes off a 1,000-square-foot roof?
One inch produces about 623 theoretical gallons; at 85% efficiency, roughly 530 gallons are captured.
Can harvested rainwater be used for drinking?
This calculator addresses volume only. Potable use requires appropriate treatment, testing and local compliance.