Rainwater Harvesting Calculator
Estimate your rainwater collection potential, determine optimal tank size, and calculate savings.
Roof & Rainfall
80%
Storage & Usage
Annual Collection Potential
28,409 gal
710 gallons per inch of rain
Usage Coverage
Coverage of Daily Usage156%
Tank Sizing
10.0
Days of Storage
700
Recommended (gal)
Consider a larger tank. Recommended: 700 gallons for 2 weeks storage.
Financial Savings
$142
Annual Savings
$12
Monthly Avg
Monthly Collection Estimate
Jan
1420
Feb
1657
Mar
2131
Apr
2367
May
2604
Jun
1894
Jul
1657
Aug
1894
Sep
2367
Oct
2841
Nov
2604
Dec
1894
Environmental Impact
28k
Gal Runoff Reduced
43
kWh Saved
30
lbs CO2 Saved
System Notes
First Flush: Divert first 15 gallons to remove roof contaminants
Effective Efficiency: 76% (accounting for roof type)
Potential Overflow: ~22409 gallons/year
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Editorial Note
MyCalcBuddy Editorial Team
This page is maintained as an educational calculator reference.
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Formula Source: Standard Mathematical References
by Various
🔄Last reviewed: May 2026
✓Formula checks are based on standard references and internal QA review.