Inches to Millimeters
One inch equals 25.4 millimeters.
Millimeters = inches × 25.4
By Piero Nanni · Last checked
Inches to Millimeters Calculator
1 Inches = 25.4 Millimeters
How to Convert Inches to Millimeters
Formula:
Millimeters = inches × 25.4
Worked example:
2 inches × 25.4 = 50.8 millimeters
Inches to Millimeters Conversion Table
| in | mm |
|---|---|
| 0.125 | 3.175 |
| 0.15 | 3.81 |
| 0.2 | 5.08 |
| 0.25 | 6.35 |
| 0.3 | 7.62 |
| 0.375 | 9.525 |
| 0.4 | 10.16 |
| 0.5 | 12.7 |
| 0.6 | 15.24 |
| 0.7 | 17.78 |
| 0.75 | 19.05 |
| 0.8 | 20.32 |
| 0.9 | 22.86 |
| 1 | 25.4 |
| 1.5 | 38.1 |
| 2 | 50.8 |
| 2.5 | 63.5 |
| 3 | 76.2 |
| 4 | 101.6 |
| 5 | 127 |
| 6 | 152.4 |
| 7 | 177.8 |
| 7.5 | 190.5 |
| 8 | 203.2 |
| 9 | 228.6 |
| 10 | 254 |
| 12 | 304.8 |
| 15 | 381 |
| 20 | 508 |
| 24 | 609.6 |
About This Conversion
Inches to millimeters is how imperial drawings get read on metric machines. CNC toolpaths, tapping sizes and material thicknesses all end up in millimeters, and the multiplication by 25.4 is exact, so no precision is lost in the conversion itself.
Fractional inputs are the usual friction. The common shop fractions convert to inconvenient metric values: 1/4 in is 6.35 mm, 3/8 in is 9.525 mm, 1/2 in is 12.7 mm. None of them land on a stock metric size, which is why mixed-standard assemblies need dedicated hardware rather than substitutions.
Frequently Asked Questions
How many millimeters are in an inch?
Exactly 25.4 millimeters, by definition.
What is 1/2 inch in mm?
Half an inch is exactly 12.7 mm.
What is 3/4 inch in mm?
Three quarters of an inch is exactly 19.05 mm.
Why do imperial fractions never match metric sizes?
Because 25.4 has factors of 2 and 5 only in awkward combinations, halving an inch repeatedly never produces a whole number of millimeters below 25.4.