Rainfall Converter
Convert rainfall depth between millimeters, centimeters, inches and liters per square meter.
· CalcFlow Editorial
1 mm = 0.039370079 in
Results shown are estimates for informational purposes only. Nothing on CalcFlow is financial, tax, legal, or medical advice. Always consult a qualified professional before making important decisions.
Common Rainfall Conversions
| Millimeters | Inches | Centimeters | Liters per square meter |
|---|---|---|---|
| 1 mm | 0.039370079 | 0.1 | 1 |
| 2 mm | 0.078740157 | 0.2 | 2 |
| 5 mm | 0.19685039 | 0.5 | 5 |
| 10 mm | 0.39370079 | 1 | 10 |
| 25.4 mm | 1 | 2.54 | 25.4 |
| 50 mm | 1.9685039 | 5 | 50 |
| 100 mm | 3.9370079 | 10 | 100 |
| 250 mm | 9.8425197 | 25 | 250 |
| 500 mm | 19.685039 | 50 | 500 |
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
- Pick the unit you have in the left selector and the unit you want in the right selector.
- Type a number in either box; the other box updates instantly.
- Use the swap button to reverse the direction and Copy result to copy the answer.
Frequently Asked Questions
How many mm is an inch of rain?
How many liters is 1 mm of rain?
How many gallons of water fall on an acre with an inch of rain?
Sources: NIST SP 811 (international inch = 25.4 mm); definition of the liter (1 L = 1 dm3).