Aisha K.
Mar 12, 2026
Clean layout and the results update instantly. Exactly what I needed for a quick planning check.
Homesteading & Micro-Gardening
Roof Catchment Rainwater Harvesting Gallon Calculator
Gal = roof sq ft × inches rain × 0.623 × efficiency.
Estimate harvested gallons from roof area and rainfall. Planning estimates only — verify measurements independently.
Inputs
10010000
0.112
50100
Smart analysis
Recommendations
Tailored to your live inputs and result—guidance only, not professional advice.
- Interpret
Treat this as a planning estimate
Primary result: Harvested water = 794 gal. Re-run with optimistic and pessimistic inputs to understand the range—not just a single point.
Scenario studio
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Scenario A
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Scenario B
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Plain-English guide
Terms & how it works
Confused by a field? Read the short definitions here while you use the tool.
Roof catchment (sq ft)
The “Roof catchment (sq ft)” value used in this tool’s formula. Adjust it to see results update live.
Rainfall (in)
The “Rainfall (in)” value used in this tool’s formula. Adjust it to see results update live.
Collection efficiency (%)
The “Collection efficiency (%)” value used in this tool’s formula. Adjust it to see results update live.
How this calculator works
Estimate harvested gallons from roof area and rainfall. Planning estimates only — verify measurements independently. Gal = roof sq ft × inches rain × 0.623 × efficiency. Example: 1,500 sq ft roof, 1 in rain, 85% efficiency → ~795 gal.
Gal = roof sq ft × inches rain × 0.623 × efficiency.
Example: 1,500 sq ft roof, 1 in rain, 85% efficiency → ~795 gal.
When to use this Roof Rainwater Harvesting
Common use cases
- Estimate harvested gallons from roof area and rainfall.
- Sanity-check with this case: 1,500 sq ft roof, 1 in rain, 85% efficiency → ~795 gal.
- The relationship is: Gal = roof sq ft × inches rain × 0.623 × efficiency.
Localized examples
- Homesteading & Micro-Gardening: the example on this page uses the same formula as the widget.
What you get
- Fields: Roof catchment (sq ft), Rainfall (in), Collection efficiency (%)
- Gal = roof sq ft × inches rain × 0.623 × efficiency.
- Example on the page: 1,500 sq ft roof, 1 in rain, 85% efficiency → ~795 gal.
How to Calculate Roof Rainwater Harvesting Step-by-Step
- 1Enter Roof catchment (sq ft), Rainfall (in), Collection efficiency (%). Use the values you have, not a catalog average, unless that is all you know.
- 2Gal = roof sq ft × inches rain × 0.623 × efficiency.
- 3Worked case: 1,500 sq ft roof, 1 in rain, 85% efficiency → ~795 gal.
- 4Order a little extra. Resin, fabric, and clay do not read a spreadsheet.
Governing formula
Gal = roof sq ft × inches rain × 0.623 × efficiency.
1,500 sq ft roof, 1 in rain, 85% efficiency → ~795 gal.
Example: set Roof catchment (sq ft) = 1,500, Rainfall (in) = 1, Collection efficiency (%) = 85, then read the result.
Variable definitions
- roofSqFt
Roof catchment (sq ft)
The “Roof catchment (sq ft)” field. Default 1500; typical range 100–10000.
- rainfallIn
Rainfall (in)
The “Rainfall (in)” field. Default 1; typical range 0.1–12.
- efficiencyPct
Collection efficiency (%)
The “Collection efficiency (%)” field. Default 85; typical range 50–100.
- Volume math (Gal = roof sq ft × inches rain × 0.623 × efficiency.) does not include your waste, test pour, or the batch that cures wrong. Add a buffer.
- Nothing here is uploaded for the calculation itself.
Frequently Asked Questions
Gal = roof sq ft × inches rain × 0.623 × efficiency.
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Community
Reviews & Ratings
See what others think about this tool, then leave your own rating to help improve CalculioHub.
4.8
out of 5.0
4 reviews
Daniel R.
Feb 28, 2026
Very usable on mobile. Would love a save/export option later, but the math feels solid.
Priya S.
Feb 3, 2026
The FAQ section answered my questions before I even had to search. Smooth dark mode too.
Marcus L.
Jan 19, 2026
Simple inputs, clear outputs. This replaced three bookmarks I used to juggle.
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