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Rainfall Inches to mm Converter — Reference Guide and Chart
Converting rainfall from inches to millimeters: multiply inches by 25.4. One inch of rain equals exactly 25.4 millimeters. The reverse: divide mm by 25.4 to get inches.
Rainfall Inches to mm Converter — Reference Guide and Chart
Converting rainfall from inches to millimeters: multiply inches by 25.4. One inch of rain equals exactly 25.4 millimeters. The reverse: divide mm by 25.4 to get inches.
Quick reference chart:
Why the conversion matters:
Most US weather apps report rainfall in inches. International services and scientific sources (Environment Canada, the European Centre for Medium-Range Weather Forecasts, NOAA research data) use millimeters. When a storm report says "50 mm of rain expected," that's just under 2 inches — significant but not extreme. Learn more in Tornado Risk Calculator — Understanding CAPE and Wind Shear. Learn more in Sunburn Time Calculator — How Long Before You Burn by UV Index.
For agriculture, irrigation, and rain gauges calibrated in mm, the 25.4 conversion is a weekly calculation. A crop that needs 1 inch of water per week needs exactly 25.4 mm. A rain event that delivers 12 mm covers about half that need.
For outdoor events, 0.10 inches (2.5 mm) is a light drizzle. Anything above 0.25 inches (6.4 mm) per hour produces puddles and mud that affect ground conditions.
