How it works
US gallons collected = roof area × rainfall × 0.623 × collection efficiency.
Input definitions
- Collection roof area (ft²)
- Enter the value in the labeled unit.
- Rainfall (in)
- Enter the value in the labeled unit.
- Collection efficiency (%)
- Enter the value in the labeled unit.
A worked example
- Collection roof area (ft²)
- 1200
- Rainfall (in)
- 1
- Collection efficiency (%)
- 85
Assumptions & limits
Uses only the values entered. Rates are illustrative inputs, not live quotes, legal rules or personalised advice. Check provider terms, local requirements and measurements before acting.
Sources & review
Maintained by AnsRio. Methods and examples use automated checks; this does not imply independent professional certification.
Method updated 2026-10-19. Content checked against the stated method and examples. Our verification approach.
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Common questions
Is all roof runoff suitable for use?
No. Water quality, first-flush diversion, roofing material and local rules determine permitted uses.
How does Rainwater harvest volume calculate the result?
US gallons collected = roof area × rainfall × 0.623 × collection efficiency.
What should I verify before using Rainwater harvest volume?
Uses only the values entered. Rates are illustrative inputs, not live quotes, legal rules or personalised advice. Check provider terms, local requirements and measurements before acting.