# Mil to mm Converter

URL: https://speedycalculator.com/calculators/conversion/mil-to-mm/
Last updated: 2026-10-25

> Convert mils (mil) to millimetres (mm): 1 mil (thou) = 0.0254 mm, so multiply by 0.0254 or divide by 39.370079. Both fields are editable, so you can also type in millimetres and get mils back.

## Inputs

- Mils (mil)

## Results

- Millimetres

## Formula

```
1 mil = 0.0254 mm
1 mm = 39.370079 mil
mm = mil × 0.0254
```

## Explanation

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

MilsMillimetresMillimetresMils1 mil0.0254 mm1 mm39.370079 mil2 mil0.0508 mm2 mm78.740157 mil4 mil0.1016 mm5 mm196.85039 mil6 mil0.1524 mm10 mm393.70079 mil10 mil0.254 mm20 mm787.40157 mil15 mil0.381 mm50 mm1,968.5039 mil20 mil0.508 mm100 mm3,937.0079 mil40 mil1.016 mm1,000 mm39,370.079 mil60 mil1.524 mm100 mil2.54 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).

## Worked example

Inputs — Mils: 10 mil.

Results — **Millimetres = 0.254 mm**.

## FAQ

**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.


## Sources

- [NIST Special Publication 811 – Guide for the Use of the International System of Units](https://www.nist.gov/pml/special-publication-811)
- [NIST Handbook 44 Appendix C – General tables of units of measurement](https://www.nist.gov/pml/owm/nist-handbook-44-current-edition)