Millimeters to Inches Converter
Convert millimeters to inches instantly. 1 mm = 0.0393701 in. Formula, table and why engineering drawings mix both units.
Written by Rahman · Last reviewed
Quick answer
One millimeter equals 0.0393701 inches. Divide millimeters by 25.4 to get inches, so a 6 mm bolt is about 0.236 inches, close to but not exactly a quarter-inch (0.25 in) fastener.
| Metre (m) | 0.001 |
| Kilometre (km) | 0.000001 |
| Decimetre (dm) | 0.01 |
| Centimetre (cm) | 0.1 |
| Millimetre (mm) | 1 |
| Micrometre (µm) | 1000 |
| Nanometre (nm) | 1000000 |
| Mile (mi) | 6.213712e-7 |
| Yard (yd) | 0.001093613298 |
| Foot (ft) | 0.003280839895 |
| Inch (in) | 0.03937007874 |
| Nautical mile (nmi) | 5.399568e-7 |
| Light year (ly) | 1.057001e-19 |
mm to in conversion table
| mm | in |
|---|---|
| 1 mm | 0.03937007874 in |
| 2 mm | 0.07874015748 in |
| 3 mm | 0.1181102362 in |
| 4 mm | 0.157480315 in |
| 5 mm | 0.1968503937 in |
| 6 mm | 0.2362204724 in |
| 7 mm | 0.2755905512 in |
| 8 mm | 0.3149606299 in |
| 9 mm | 0.3543307087 in |
| 10 mm | 0.3937007874 in |
| 20 mm | 0.7874015748 in |
| 30 mm | 1.181102362 in |
| 40 mm | 1.57480315 in |
| 50 mm | 1.968503937 in |
| 60 mm | 2.362204724 in |
| 70 mm | 2.755905512 in |
| 80 mm | 3.149606299 in |
| 90 mm | 3.543307087 in |
| 100 mm | 3.937007874 in |
| 250 mm | 9.842519685 in |
| 500 mm | 19.68503937 in |
| 1000 mm | 39.37007874 in |
How to convert mm to in
Fastener sizes are the classic case where this conversion matters in practice: a US "quarter-inch" bolt is 6.35 mm, while a metric M6 bolt is 6 mm, close enough to jam into the wrong hole but different enough to strip the thread. Mechanics keep a conversion chart specifically because "close" is not "compatible" in hardware.
Smartphone and laptop screens are typically specified with a thickness or bezel width in millimetres even in US marketing copy, because component tolerances in manufacturing are set in millimetres globally, and the inch figure, when quoted at all, is a converted afterthought rather than the design unit. Camera lens focal lengths are specified in millimetres worldwide regardless of where the camera is sold, one of the few measurements where the metric figure is universal even on US product pages.