This page converts microns into mils using the factor 0.03937007874, and shows the reverse figure alongside it. Both units measure length, which is why one number does the whole job.
The older name for a micrometre, still standard in filtration, machining and paint-thickness specifications. One thousandth of an inch, the standard thickness unit for plastic film and PCB traces.
The mil and the millimetre are not the same thing and are out by a factor of about forty. A mil is one thousandth of an inch — 0.0254 mm — and a spec sheet that quotes film thickness in mils means the small unit. British drawings write the same size as "thou". Below the calculator there is a step table for the values people look up most, and a second table putting real length figures into mils so the number you get has something to be compared against.
The formula
microns- The amount you are converting, in microns
0.0393700787402- The exact number of mils in one micron
mils- The converted result
How it works, step by step
- Enter the value in microns.
- It is multiplied by 0.0393700787402, the exact factor between the two units.
- The answer is shown in mils, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
A door height: 2.03e+06 micron in mils
At 2.03e+06 micron (a door height), the same quantity in mils is 2.03e+06 × 0.0393701 = 79,921.3 mil. One micron is 0.0393701 mils, so the numbers shrink as expected.
A credit card’s long edge: 8.56e+04 micron in mils
Take a credit card’s long edge, roughly 8.56e+04 micron. The conversion is a single multiplication — 8.56e+04 × 0.0393701 — giving 3370.08 mil. Because the relationship is proportional, doubling the input doubles the answer to 6740.16 mil.
How to read your score
Frequently asked questions
How many mils are in one micron?
Exactly 0.0393700787402. Every figure on this page is that one number multiplied by your input, so the only rounding is at the display step.
What is the formula to convert microns to mils?
mils = microns × 0.0393700787402. Reversed, microns = mils ÷ 0.0393700787402, which is the same as multiplying by 25.4.
Which is the bigger unit, the micron or the mil?
The mil. One micron is only 0.0393701 of a mil, so it takes 25.4 microns to make one mil.
What does this quantity actually measure?
Both units measure length. That is why a single factor is enough: there is no temperature offset and no material property involved, unlike conversions that cross between different quantities.
What is a micron?
The older name for a micrometre, still standard in filtration, machining and paint-thickness specifications.
What is a mil?
One thousandth of an inch, the standard thickness unit for plastic film and PCB traces.
Why does my answer differ from another converter?
Almost always because the other tool rounded the factor before multiplying. This page keeps full double precision through the calculation and rounds only for display, and it prints the factor it used so you can see where any difference came from.
Is there a quick way to do micron to mil in my head?
Plenty of people do this in their head: divide by 25 instead of using the exact factor 0.03937007874. At 100 that shortcut gives 4 mils, off by 0.06299 mils or about 1.60%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Microns to mils reference tables
| Microns | Mils |
|---|---|
| 0.5 micron | 0.019685 mil |
| 1 micron | 0.0393701 mil |
| 2 micron | 0.0787402 mil |
| 3 micron | 0.11811 mil |
| 5 micron | 0.19685 mil |
| 10 micron | 0.393701 mil |
| 20 micron | 0.787402 mil |
| 25 micron | 0.984252 mil |
| 50 micron | 1.9685 mil |
| 75 micron | 2.95276 mil |
| 100 micron | 3.93701 mil |
| 250 micron | 9.84252 mil |
| 500 micron | 19.685 mil |
| 1000 micron | 39.3701 mil |
| 5000 micron | 196.85 mil |
Exact factor: 1 micron = 0.0393700787402 mils.
| Quantity | micron | mil |
|---|---|---|
| A credit card’s long edge | 8.56e+04 micron | 3370 mil |
| A door height | 2.032e+06 micron | 8e+04 mil |
| An Olympic pool | 5e+07 micron | 1.969e+06 mil |
| The Eiffel Tower | 3.3e+08 micron | 1.299e+07 mil |
| A marathon | 4.22e+10 micron | 1.661e+09 mil |
| Earth’s diameter | 1.274e+13 micron | 5.017e+11 mil |
Published reference values, converted with the same factor this page uses.