Mm to inches
One millimeter is 0.0393701 inches. Type a length in millimeters to see it in inches.
How to convert millimeters to inches
Formula: inches = millimeters ÷ 25.4
For example, 50 mm is 1.97 in. The figure is exact. Since 1959 the inch has been defined as precisely 25.4 millimeters, so the only rounding is in how many decimals you keep.
A quick way to do it in your head
Multiply the millimeters by 4, then move the decimal point two places to the left.
- 10 mm: 10 × 4 = 40, so about 0.4 in. The true answer is 0.39 in.
- 50 mm: 50 × 4 = 200, so about 2 in. The true answer is 1.97 in.
- 300 mm: 300 × 4 = 1200, so about 12 in. The true answer is 11.81 in.
The shortcut always runs about 1.6% high. That is close enough for choosing a shelf or a picture frame, and not close enough for a drill bit.
Millimeters to inches table
| Millimeters | Inches |
|---|---|
| 1 mm | 0.039 in |
| 2 mm | 0.079 in |
| 3 mm | 0.118 in |
| 4 mm | 0.157 in |
| 5 mm | 0.197 in |
| 6 mm | 0.236 in |
| 8 mm | 0.315 in |
| 10 mm | 0.39 in |
| 12 mm | 0.47 in |
| 15 mm | 0.59 in |
| 20 mm | 0.79 in |
| 25 mm | 0.98 in |
| 30 mm | 1.18 in |
| 40 mm | 1.57 in |
| 50 mm | 1.97 in |
| 75 mm | 2.95 in |
| 100 mm | 3.94 in |
| 150 mm | 5.91 in |
| 200 mm | 7.87 in |
| 300 mm | 11.81 in |
| 500 mm | 19.69 in |
| 1,000 mm | 39.37 in |
Inch fractions in millimeters
Drill bits, bolts, sockets and plywood are sold in fractions of an inch in the United States and in whole millimeters almost everywhere else. This table goes the other way, from the fraction to the millimeters.
| Inches | As a decimal | Millimeters |
|---|---|---|
| 1/16 in | 0.0625 in | 1.5875 mm |
| 1/8 in | 0.125 in | 3.175 mm |
| 3/16 in | 0.1875 in | 4.7625 mm |
| 1/4 in | 0.25 in | 6.35 mm |
| 5/16 in | 0.3125 in | 7.9375 mm |
| 3/8 in | 0.375 in | 9.525 mm |
| 1/2 in | 0.5 in | 12.7 mm |
| 5/8 in | 0.625 in | 15.875 mm |
| 3/4 in | 0.75 in | 19.05 mm |
| 7/8 in | 0.875 in | 22.225 mm |
| 1 in | 1 in | 25.4 mm |
Near misses matter here. A 10 mm socket is not a 3/8 in socket: 3/8 in is 9.525 mm, almost half a millimeter smaller, which is enough to round off a bolt head.
Sizes you are likely to meet
| What | Millimeters | Inches |
|---|---|---|
| The small headphone plug | 3.5 mm | 0.138 in |
| The large headphone plug | 6.35 mm | 0.25 in, exactly 1/4 |
| 35 mm film, width | 35 mm | 1.38 in |
| A 50 mm camera lens, focal length | 50 mm | 1.97 in |
| A4 paper | 210 × 297 mm | 8.27 × 11.69 in |
| US Letter paper | 215.9 × 279.4 mm | 8.5 × 11 in |
For longer lengths, use cm to inches. To go the other way, the unit converter has inches to millimeters under Length.
Questions
How many inches is 1 mm?
0.0393701 in, or a little under 1/25 of an inch.
How many mm are in an inch?
Exactly 25.4 mm.
How many inches is 10 mm?
0.394 in, slightly more than 3/8 in.
How many inches is 25 mm?
0.984 in, just under one inch.
How many inches is 100 mm?
3.94 in.
What is 1/8 inch in mm?
3.175 mm.
Is it millimeters or millimetres?
Both are correct. “Millimeter” is the American spelling and “millimetre” is used in most other English-speaking countries. The unit is the same.