Millimeters meet inches wherever metric products land in imperial workshops — drill bits, screws, phone cases, pipe fittings, and 3D-printer nozzles are all sold in one system and used in another. One millimeter equals 0.0393701 inches, and the conversion is exact: 25.4 mm is precisely one inch. Whether you are shopping for hardware online, reading a spec sheet, or scaling a model, getting the inch value right avoids an ill-fitting part. Type any millimeter measurement into the converter below for the exact inch equivalent.
Mm to Inches Converter
Result will appear here
Mm to Inches Conversion Formula
The inch is defined as exactly 25.4 millimeters by international agreement, so one millimeter is 1 ÷ 25.4 = 0.0393701 inches. Multiply any millimeter value by 0.0393701 and you get inches. Unlike many conversions, this one is exact rather than approximate — the definition leaves no room for regional drift.
in = mm × 0.0393701
Example: 50 mm × 0.0393701 = 1.9685 in — a 50 mm bolt is about 1.9685 inches long.
To convert back: mm = in ÷ 0.0393701 (or multiply inches by 25.4).
How to Convert Mm to Inches
- Enter your millimeter value in the converter above.
- The inch equivalent shows up immediately as you type.
- Press Swap to go the other way, from inches to millimeters.
- For pen-and-paper math, multiply millimeters by 0.0393701.
Mm to Inches Conversion Chart
Find your millimeter measurement on the left and read the inch equivalent on the right. The table covers 1–10 mm for fine hardware, plus 25, 50, and 100 mm — the range where most screws, drill bits, and fittings live — so you can match metric parts to imperial specs at a glance.
| Millimeters (mm) | Inches (in) |
| 1 | 0.0394 |
| 2 | 0.0787 |
| 3 | 0.1181 |
| 4 | 0.1575 |
| 5 | 0.1969 |
| 6 | 0.2362 |
| 7 | 0.2756 |
| 8 | 0.315 |
| 9 | 0.3543 |
| 10 | 0.3937 |
| 25 | 0.9843 |
| 50 | 1.9685 |
| 100 | 3.937 |
FAQs
What is the formula to convert mm to inches?
Multiply millimeters by 0.0393701: in = mm × 0.0393701. For a quick mental estimate, remember that 25 mm is roughly an inch — then refine with the calculator when the fit matters, since 25 mm is actually 0.9843 inches.
How many inches are in 1 millimeter?
One millimeter equals 0.0393701 inches — about one twenty-fifth of an inch. It is a small unit: stack 25 of them and you have just under an inch (0.9843 in, to be precise).
How many millimeters are in 1 inch?
Exactly 25.4 millimeters. This is the international definition of the inch, agreed in 1959, so it is identical everywhere — an inch in a US hardware store is the same length as an inch in a European catalog.
Which is bigger, a millimeter or an inch?
The inch is bigger — 25.4 times bigger, in fact. Millimeters handle fine detail like screw threads and paper thickness, while inches cover everyday object sizes. Most rulers show both for exactly this reason.
Where is the mm-to-inches conversion used in real life?
In hardware shopping (an M6 bolt is 6 mm, or 0.2362 in), screen and tire sizes, 3D printing (layer heights are quoted in mm, nozzle sizes sometimes in inches), photography filter threads, and bike parts — anywhere metric and imperial catalogs overlap.