Inches to Millimeters Converter
Formula
mm = inches × 25.4
To convert inches to millimeters, multiply by 25.4. This is an exact conversion.
How to use
- Enter the number of Inches you want to convert.
- Read the result in millimeters below.
- Adjust the value for any other measurement.
Example
Convert 1 inch: 1 × 25.4 = 25.4 mm. So one inch equals exactly 25.4 millimeters.
Frequently Asked Questions
How many mm is 1 inch?
1 inch = exactly 25.4 mm.
How many mm is 1/2 inch?
0.5 inches = 12.7 mm.
How do I convert millimeters back to inches?
Divide the millimeter value by 25.4, which reverses the inches-to-mm conversion. For example, 50 mm divided by 25.4 is about 1.97 inches. This is handy when a part is spec'd in mm but your tools and rulers are marked in inches.
What is a common screw or bolt size in millimeters versus inches?
A 1/4 inch fastener is 6.35 mm, and a 1/2 inch fastener is 12.7 mm, which is why metric and imperial hardware almost never interchange cleanly. Even close pairs like an M6 bolt (6 mm) and a 1/4 inch bolt (6.35 mm) differ by about 0.35 mm, enough to cross-thread or jam. Always confirm whether a part is metric or imperial before mixing them.