This inches to mm converter turns inches into millimeters as you type, using the exact factor. It is the conversion machinists, woodworkers and 3D printing hobbyists need when a plan gives fractions of an inch and the calipers, drill bits or slicer software work in millimeters. It runs in your browser and spends no credits.
How many mm are in an inch
One inch is exactly 25.4 millimeters. The figure is a definition, agreed internationally in 1959, so a converted value is as precise as the number you type in.
Inches to mm formula
Multiply the inches by 25.4:
mm = in × 25.4
Fractions have to become decimals first: divide the top number by the bottom one. 3/8 in is 0.375 in, and 0.375 × 25.4 = 9.525 mm. Type the decimal in the converter and it does the rest.
Fractional inches to mm chart
| Inches | Decimal | Millimeters |
|---|---|---|
| 1/16 in | 0.0625 | 1.5875 mm |
| 1/8 in | 0.125 | 3.175 mm |
| 3/16 in | 0.1875 | 4.7625 mm |
| 1/4 in | 0.25 | 6.35 mm |
| 5/16 in | 0.3125 | 7.9375 mm |
| 3/8 in | 0.375 | 9.525 mm |
| 1/2 in | 0.5 | 12.7 mm |
| 5/8 in | 0.625 | 15.875 mm |
| 3/4 in | 0.75 | 19.05 mm |
| 7/8 in | 0.875 | 22.225 mm |
| 1 in | 1 | 25.4 mm |
| 1.5 in | 1.5 | 38.1 mm |
| 2 in | 2 | 50.8 mm |
| 3 in | 3 | 76.2 mm |
| 6 in | 6 | 152.4 mm |
| 12 in | 12 | 304.8 mm |
Worked example: does a metric bolt fit?
A shelf bracket calls for 1/4 in screws and you have M6 screws, which are 6 mm across. 1/4 in is 6.35 mm, so the M6 is 0.35 mm thinner: it will pass through a 1/4 in hole but won’t thread into a 1/4 in nut. The same logic works for plywood: a sheet sold as 3/4 in is 19.05 mm on paper, though actual panel thickness often differs from the nominal size, so measure before you cut.
Inches and mm on the same ruler
Many tape measures carry both scales. Each 1/16 in tick is about 1.6 mm, so two marks on the inch side are a little more than three on the millimeter side. When precision matters, typing the value is faster than counting ticks.
FAQ
How many mm is half an inch?
12.7 mm exactly.
Can I type a fraction like 5/8?
Type it as a decimal, 0.625. The result is 15.875 mm.
What does it cost?
It comes with the Nexin library: Nexin Lite or Nexin Pro opens it, and it spends no credits.
