Inches to Millimeters Converter
1 in equals 25.4 mm, and 1 mm equals 0.039370079 in. Enter a value in either box to convert inches to millimeters and back. Formula: meters of depth = value x unit factor (1 in = 25.4 mm exactly; 1 mm of rain = 1 L per m2).
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1 in = 25.4 mm
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Inches to Millimeters Conversion Table
| Inches | Millimeters |
|---|---|
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 25.4 in | 645.16 mm |
| 50 in | 1,270 mm |
| 100 in | 2,540 mm |
| 250 in | 6,350 mm |
| 500 in | 12,700 mm |
Millimeters to Inches Conversion Table
| Millimeters | Inches |
|---|---|
| 1 mm | 0.039370079 in |
| 2 mm | 0.078740157 in |
| 5 mm | 0.19685039 in |
| 10 mm | 0.39370079 in |
| 25.4 mm | 1 in |
| 50 mm | 1.9685039 in |
| 100 mm | 3.9370079 in |
| 250 mm | 9.8425197 in |
| 500 mm | 19.685039 in |
Worked example: 10 in = 254 mm. 50 mm of rain is 50 / 25.4 = 1.97 inches. On a 40 m2 roof that is 40 x 50 = 2,000 liters of water.
Need other units? Open the full Rainfall Converter.
Popular Rainfall Conversions
Formula
meters of depth = value x unit factor (1 in = 25.4 mm exactly; 1 mm of rain = 1 L per m2)Understanding Rainfall Conversion
Rainfall is reported as the depth of water that would collect on flat ground. Meteorological services outside the US use millimeters, while US reports use inches. One millimeter of rain is the same as one liter of water spread over one square meter, which is why the two units give identical numbers. One inch of rain is exactly 25.4 millimeters.
Tips and Best Practices
- 1Divide millimeters by 25.4 to get inches.
- 21 mm of rain on 1 m2 is 1 liter.
- 3A roof area in square meters times millimeters of rain gives liters collected.
Real-World Example
50 mm of rain is 50 / 25.4 = 1.97 inches. On a 40 m2 roof that is 40 x 50 = 2,000 liters of water.
Common Mistakes to Avoid
- Assuming 1 inch of snow equals 1 inch of rain; snow is usually ten times as deep as its water equivalent.
- Forgetting that rainfall depth does not depend on area but total volume does.
- Mixing monthly totals with single-event totals.
How to Use
- Type a number in the Inches box.
- The Millimeters result appears instantly; you can also edit the Millimeters box to convert backwards.
- Use the swap button to reverse the direction and Copy result to copy the answer.
Frequently Asked Questions
How many millimeters are in 1 in?
How many inches are in 1 mm?
What is the formula to convert inches to millimeters?
How many liters is 1 mm of rain?
Sources: NIST SP 811 (international inch = 25.4 mm); definition of the liter (1 L = 1 dm3).