Rainfall to Gallons Calculator — Gallons of Rain Over an Area
Enter the rainfall amount (inches) and the area it falls on (square feet) to calculate how many gallons of water that rainfall delivers. Useful for understanding how much free water your garden or roof receives.
What this calculator determines
It calculates how many gallons of water a given amount of rainfall delivers over a specified area.
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Examples
1 in rain over 200 sq ft
1 in rain, 200 sq ft
Calculation
- Gallons: 1 × 200 × 0.623 = 124.7 gal
124.7 gallons
Assumptions & Conventions
- Conversion factor
- 1 inch of rain over 1 square foot = 0.623 gallons; gallons = rainfall × area × 0.623.
- Gross rainfall
- Reports total rainfall over the area before any collection losses — use the Rain Barrel Collection Calculator for captured amounts.