Multiply mils by 0.0254 to get millimetres. The two are easily confused, but a millimetre is almost 40 times thicker than a mil.
How to use the Mil to mm Converter
- Type the number of mils into the Mils field. Decimals such as 5 are fine.
- Read the answer in Millimetres – it updates as you type, with no button to press.
- To convert the other way, type into Millimetres and the mils are recalculated.
- Press Copy results to copy both values with the page title, or Copy link to share this exact conversion.
This page converts only mil ⇄ mm. Need a different unit? Use the general length converter, where you can choose any “from” and “to” unit.
How it works
Both units measure length, so they are always in the same ratio: one mil (thou) equals 0.0254 millimetres. The calculator multiplies the number of mils you type by 0.0254 to give millimetres, and when you type into the millimetres field it divides by the same factor to give mils. Because the ratio never changes, doubling the mils always doubles the millimetres. Results are calculated at full precision and rounded only for display (up to eight decimal places, with very large or small values shown in scientific notation).
How to convert mils to millimetres
- Write down the value in mils, for example 10 mil.
- Multiply by the conversion factor 0.0254 (because 1 mil (thou) = 0.0254 mm).
- 10 × 0.0254 = 0.254 mm.
- To go back from millimetres to mils, divide by 0.0254 – or multiply by 39.370079.
mil to mm conversion table
| Mils | Millimetres | Millimetres | Mils |
|---|---|---|---|
| 1 mil | 0.0254 mm | 1 mm | 39.370079 mil |
| 2 mil | 0.0508 mm | 2 mm | 78.740157 mil |
| 4 mil | 0.1016 mm | 5 mm | 196.85039 mil |
| 6 mil | 0.1524 mm | 10 mm | 393.70079 mil |
| 10 mil | 0.254 mm | 20 mm | 787.40157 mil |
| 15 mil | 0.381 mm | 50 mm | 1,968.5039 mil |
| 20 mil | 0.508 mm | 100 mm | 3,937.0079 mil |
| 40 mil | 1.016 mm | 1,000 mm | 39,370.079 mil |
| 60 mil | 1.524 mm | ||
| 100 mil | 2.54 mm |
What is a mil?
A mil (or thou) is one thousandth of an inch, 25.4 µm. It is used in North America for plastic film, garbage bags, paint and coating thickness and circuit-board traces; it is not a millimetre.
What is a millimetre?
A millimetre is one thousandth of a metre. Engineering drawings, construction plans, rainfall, screws, bolts and jewellery are all dimensioned in millimetres.
Quick mental conversion
For a fast estimate, multiply mils by about 0.025 to get millimetres; the error is about 1.6%. Use the calculator above when you need the exact figure.
Common mistakes to avoid
Mixing the international foot (0.3048 m) with the old u.s. survey foot, confusing nautical and statute miles, and writing decimal feet such as 5.5 ft as “5 ft 5 in” (it is 5 ft 6 in).
Formula
1 mil = 0.0254 mm1 mm = 39.370079 milmm = mil × 0.0254Worked example
Inputs — Mils: 10 mil.
Results — Millimetres = 0.254 mm.
Frequently asked questions
How many mm is 10 mil?
0.254 mm.
How many mil is 1 mm?
About 39.37 mil.
How do I convert mils to millimetres?
Multiply the number of mils by 0.0254. For example, 10 mil × 0.0254 = 0.254 mm.
How do I convert millimetres back to mils?
Divide by 0.0254 (or multiply by 39.370079), or simply type the value into the millimetres field above.
What is 100 mil in millimetres?
100 mil = 2.54 mm.
What is 2 mil in millimetres?
2 mil = 0.0508 mm.
Is this conversion exact?
Yes. The factor comes from the official definitions of both units (NIST and the SI), so the only difference you may see is rounding in the last displayed digit.
Can I convert to other units on this page?
This page converts only between mils and millimetres. To pick any length unit, use the general length converter linked under Related calculators.
What formula does the Mil to mm Converter use?
1 mil = 0.0254 mm.