A mil (one thousandth of an inch) is exactly 25.4 µm. Coating, film and gasket thicknesses are quoted in microns in metric specs and in mils in U.S. specs.
How to use the Micron to Mil Converter
- Type the number of micrometres into the Micrometres field. Decimals such as 12.7 are fine.
- Read the answer in Mils – it updates as you type, with no button to press.
- To convert the other way, type into Mils and the micrometres 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 µm ⇄ mil. 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 micrometre equals 0.039370079 mils. The calculator multiplies the number of micrometres you type by 0.039370079 to give mils, and when you type into the mils field it divides by the same factor to give micrometres. Because the ratio never changes, doubling the micrometres always doubles the mils. 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 micrometres to mils
- Write down the value in micrometres, for example 25.4 µm.
- Multiply by the conversion factor 0.039370079 (because 1 micrometre = 0.039370079 mil).
- 25.4 × 0.039370079 = 1 mil.
- To go back from mils to micrometres, divide by 0.039370079 – or multiply by 25.4.
µm to mil conversion table
| Micrometres | Mils | Mils | Micrometres |
|---|---|---|---|
| 1 µm | 0.039370079 mil | 1 mil | 25.4 µm |
| 5 µm | 0.19685039 mil | 2 mil | 50.8 µm |
| 10 µm | 0.39370079 mil | 5 mil | 127 µm |
| 25 µm | 0.98425197 mil | 10 mil | 254 µm |
| 25.4 µm | 1 mil | 20 mil | 508 µm |
| 50 µm | 1.9685039 mil | 50 mil | 1,270 µm |
| 75 µm | 2.9527559 mil | 100 mil | 2,540 µm |
| 100 µm | 3.9370079 mil | 1,000 mil | 25,400 µm |
| 150 µm | 5.9055118 mil | ||
| 200 µm | 7.8740157 mil | ||
| 250 µm | 9.8425197 mil | ||
| 500 µm | 19.685039 mil |
What is a micrometre?
A micrometre, usually called a micron, is one millionth of a metre. It measures fibres, cells, filter ratings, coatings and fine particles such as PM2.5 dust.
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.
Quick mental conversion
For a fast estimate, multiply micrometres by about 0.039 to get mils; the error is about 0.9%. 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 µm = 0.039370079 mil1 mil = 25.4 µmmil = µm × 0.039370079Worked example
Inputs — Micrometres: 25.4 µm.
Results — Mils = 1 mil.
Frequently asked questions
How many microns is 1 mil?
25.4 µm.
How many mils is 100 µm?
About 3.94 mil.
How do I convert micrometres to mils?
Multiply the number of micrometres by 0.039370079. For example, 25.4 µm × 0.039370079 = 1 mil.
How do I convert mils back to micrometres?
Divide by 0.039370079 (or multiply by 25.4), or simply type the value into the mils field above.
What is 10 µm in mils?
10 µm = 0.39370079 mil.
What is 100 µm in mils?
100 µm = 3.9370079 mil.
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 micrometres and mils. To pick any length unit, use the general length converter linked under Related calculators.
What formula does the Micron to Mil Converter use?
1 µm = 0.039370079 mil.