Convert Inches to Millimeters
1 Inch (in) = 25.4 Millimeters (mm). Use the free converter below to instantly convert any inch value to millimeters, or view the full conversion table and formula.
1 in = 25.4 mm
Inch to Millimeter Conversion Table
How to Convert Inches to Millimeters
To convert inches to millimeters, multiply by 25.4. This is an exact conversion factor — 1 inch is defined as precisely 25.4 mm. For example, 3 inches × 25.4 = 76.2 mm. This is essential for engineering, machining, and any work requiring metric precision.
Worked Example: Convert 4 in to mm
Start with the value in inches
4 in
Apply the formula
mm = 4 × 25.4
Calculate the result
4 in = 101.6 mm
Inch to Millimeter Examples
1 in is equal to 25.4 mm. Using the formula inches × 25.4, 1 in converts to 25.4 mm.
2 in is equal to 50.8 mm. Using the formula inches × 25.4, 2 in converts to 50.8 mm.
3 in is equal to 76.2 mm. Using the formula inches × 25.4, 3 in converts to 76.2 mm.
4 in is equal to 101.6 mm. Using the formula inches × 25.4, 4 in converts to 101.6 mm.
5 in is equal to 127 mm. Using the formula inches × 25.4, 5 in converts to 127 mm.
6 in is equal to 152.4 mm. Using the formula inches × 25.4, 6 in converts to 152.4 mm.
7 in is equal to 177.8 mm. Using the formula inches × 25.4, 7 in converts to 177.8 mm.
8 in is equal to 203.2 mm. Using the formula inches × 25.4, 8 in converts to 203.2 mm.
Converting Millimeters to Inches
Need the reverse conversion? Use the table below for a quick reference converting millimeters back to inches.
| Millimeters (mm) | Inches (in) |
|---|---|
| 1 | 0.0394 |
| 2 | 0.0787 |
| 3 | 0.1181 |
| 5 | 0.1969 |
| 10 | 0.3937 |
| 15 | 0.5906 |
Inches to Millimeters FAQ
How many mm is 1 inch?
1 inch equals exactly 25.4 millimeters. This is an exact definition, not an approximation.
What is 1/4 inch in mm?
1/4 inch (0.25 inches) equals exactly 6.35 millimeters.
Understanding Inches and Millimeters
What is an Inch (in)?
The inch (in) is a unit of length in the imperial system. It is commonly abbreviated as in and relates to millimeters by a factor of 25.4.
What is a Millimeter (mm)?
The millimeter (mm) is a unit of length in the metric system. It is commonly abbreviated as mm and relates to inches by a factor of 0.03937.