MM to Inches formula
1 millimetre = 0.03937007874 inches, and 1 inch = 25.4 millimetres. One thousandth of a metre.
MM to Inches chart
| Millimetres (mm) | Inches (in) |
|---|---|
| 1 | 0.0394 |
| 2 | 0.0787 |
| 3 | 0.1181 |
| 4 | 0.1575 |
| 5 | 0.1969 |
| 6 | 0.2362 |
| 8 | 0.315 |
| 10 | 0.3937 |
| 12 | 0.4724 |
| 15 | 0.5906 |
| 16 | 0.6299 |
| 19 | 0.748 |
| 20 | 0.7874 |
| 25 | 0.9843 |
| 25.4 | 1 |
| 30 | 1.1811 |
| 35 | 1.378 |
| 40 | 1.5748 |
| 50 | 1.9685 |
| 60 | 2.3622 |
| 75 | 2.9528 |
| 100 | 3.937 |
| 150 | 5.9055 |
| 200 | 7.874 |
| 300 | 11.811 |
Values are rounded to 4 decimal places. The converter above shows more precision.
Worked examples
A 6 mm drill bit
6 mm ÷ 25.4 = 0.2362 in
6 millimetres = 0.2362 inches. That is 0.236 inches, a hair over the 15/64-inch bit (0.234 in) in an imperial set. For a tight wall-plug hole, use the metric bit the plug asks for.
50 mm of rain in a day
50 mm ÷ 25.4 = 1.9685 in
50 millimetres = 1.9685 inches. Nearly 2 inches of rain, a heavy downpour that can cause local flooding. Weather services in the US report rainfall in inches.
Converting millimetres to inches in real life
Millimetres are the unit for anything small and precise: drill bits, bolts and spanners, camera lenses, bike parts, phone thickness, rain gauges and jewellery. Inches show up when you shop at a US hardware store or read American plans, where sizes are often fractions such as 1/4, 3/8 or 5/16 of an inch.
Metric and imperial tools rarely match exactly. A 10 mm socket is 0.394 inches, between 3/8 (0.375) and 13/32 (0.406), so it will not fit a 3/8-inch bolt properly. When a fit matters, always use the tool made for that system. For longer lengths, centimetres are easier to read: see cm to inches.