Convert Millimeter to Mil
Convert millimeters to mils instantly. 1 millimeter = 39.3700787402 mil — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Mil to Millimeter converter for the reverse conversion.
Units explained
Millimeter
A millimeter is a metric unit of length equal to one thousandth of a meter (1/1000 m). It is the standard small-scale unit in the SI system and is widely used wherever sub-centimeter precision matters.
The millimeter was defined alongside the meter when France adopted the metric system in 1795, using the standard SI prefix milli- (from Latin mille, "thousand") to denote one-thousandth.
Millimeters are used in engineering drawings, machining, manufacturing, paper sizes, rainfall measurement, and any context where dimensions below one centimeter need to be specified clearly. Most rulers worldwide are marked in millimeters.
Adopted in 1795 in France as part of the original metric system; standardized internationally by the Metre Convention in 1875 and confirmed in the SI in 1960.
Mil
A mil (also called a thou) is an Imperial unit of length equal to one thousandth of an inch (1/1000 in = 0.0254 mm = 25.4 μm exactly). It is used in engineering, manufacturing, and materials specifications.
The mil is derived from the Latin mille, "thousand," denoting one-thousandth of an inch. Standardized in industrial use during the 19th-century rise of precision engineering.
Mils are used to specify thicknesses of plastic films, foils, paper, copper traces on printed circuit boards (PCBs), wire insulation, and paint coatings. A standard sheet of paper is about 4 mils thick.
Adopted in 19th-century engineering practice; the value (1/1000 in) became exact in 1959 when the inch was fixed at 25.4 mm via the International Yard and Pound Agreement. The British term is "thou"; American term is "mil".
Millimeter to Mil conversion formula
The relationship between millimeters and mils:
To convert millimeters to mils, multiply the value in millimeters by 39.3700787402. To reverse, multiply mils by 0.0254.
How to use this converter
Type a value into the calculator. The result in mils updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Mil to Millimeter converter for the reverse direction.
Step-by-step: convert millimeters to mils
- Write down the value in millimeters (mm).
- Multiply that value by the factor 39.3700787402.
- The product is the equivalent value in mils (mil).
- To reverse, multiply the mil value by 0.0254.
Worked examples
Example 1 — Convert 1 mm to mil:
1 × 39.3700787402 = 39.3700787402 mil
Example 2 — Convert 100 mm to mil:
100 × 39.3700787402 = 3937.0078740157 mil
Real-world example — One millimeter to mils
1 mm equals 39.37 mils — the everyday conversion for international packaging buyers translating millimeter-scale European film thickness specs into the mil units used by US suppliers and inspectors.
1 mm × 39.3700787402 = 39.3700787402 mil
Real-world example — Paper thickness in mils
A 0.5-mm paper thickness equals 19.69 mils. International printing buyers reconcile metric (mm) and US (mil) paper-thickness specs every time they place a cross-border order.
0.5 mm × 39.3700787402 = 19.6850393701 mil
Real-world example — Foam-padding gauge
2 mm of foam padding equals 78.74 mils. Cushion and gasket manufacturers translate between metric and imperial sub-millimeter units constantly because the materials catalogue often mixes both.
2 mm × 39.3700787402 = 78.7401574803 mil
Millimeter to Mil conversion table
Standard reference values for converting millimeters to mils:
| Millimeter [mm] | Mil [mil] |
|---|---|
| 0.01 | 0.3937007874 |
| 0.1 | 3.937007874 |
| 1 | 39.3700787402 |
| 2 | 78.7401574803 |
| 3 | 118.1102362205 |
| 4 | 157.4803149606 |
| 5 | 196.8503937008 |
| 10 | 393.7007874016 |
| 20 | 787.4015748031 |
| 30 | 1181.1023622047 |
| 40 | 1574.8031496063 |
| 50 | 1968.5039370079 |
| 100 | 3937.0078740157 |
| 500 | 19685.0393700787 |
| 1000 | 39370.0787401575 |
Frequently asked questions
How many mils is 1 millimeter?
How do I convert millimeters to mils?
How do I convert mils back to millimeters?
How many mils is 100 millimeters?
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Imperial / US Customary (27 units)
Nautical (1 units)
Astronomical (9 units)
Atomic / Physics (6 units)
Typographic (3 units)
Sources & references
Conversion factor (1 mm = 39.3700787402 mil) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- NIST — Refinement of values for the yard and pound (Federal Register 1959)
The treaty (signed by US
- International Astronomical Union — System of Astronomical Constants
The IAU defines astronomical units including the AU (149597870700 m exactly) light-year and parsec used in astronomy and astrophysics.