Inches to Millimeters (in to mm)
Multiply inches by 25.4 to get millimeters. For fractional inches, convert the fraction to a decimal first: 3/8 in = 0.375 in = 9.525 mm.
Millimeters
25.4
Formula
millimeters = inches × 25.4
Example: 0.375 inches = 9.525 millimeters.
Inches to Millimeters chart
| inches | millimeters |
|---|---|
| 0.0625 | 1.5875 |
| 0.125 | 3.175 |
| 0.25 | 6.35 |
| 0.375 | 9.525 |
| 0.5 | 12.7 |
| 0.625 | 15.875 |
| 0.75 | 19.05 |
| 1 | 25.4 |
| 1.5 | 38.1 |
| 2 | 50.8 |
| 3 | 76.2 |
| 4 | 101.6 |
| 6 | 152.4 |
| 12 | 304.8 |
Good to know
Common fractions: 1/16 in = 1.5875 mm, 1/8 = 3.175 mm, 1/4 = 6.35 mm, 3/8 = 9.525 mm, 1/2 = 12.7 mm, 5/8 = 15.875 mm, 3/4 = 19.05 mm.
Pipe sizes are an exception: a '1/2 inch' pipe is a nominal size, and its actual outside diameter is larger. Check the manufacturer's table for plumbing parts.
Frequently asked questions
How many mm is 1 inch?
Exactly 25.4 mm.
How many mm is 3/8 inch?
3/8 in is 9.525 mm.
How many mm is 1/2 inch?
1/2 in is 12.7 mm.