Convert Mil to Millimeter
Convert mils to millimeters instantly. 1 mil = 0.0254 millimeter — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Millimeter to Mil converter for the reverse conversion.
Units explained
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
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 to Millimeter conversion formula
The relationship between mils and millimeters:
To convert mils to millimeters, multiply the value in mils by 0.0254. To reverse, multiply millimeters by 39.3700787402.
How to use this converter
Type a value into the calculator. The result in millimeters updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Millimeter to Mil converter for the reverse direction.
Step-by-step: convert mils to millimeters
- Write down the value in mils (mil).
- Multiply that value by the factor 0.0254.
- The product is the equivalent value in millimeters (mm).
- To reverse, multiply the millimeter value by 39.3700787402.
Worked examples
Example 1 — Convert 1 mil to mm:
1 × 0.0254 = 0.0254 mm
Example 2 — Convert 100 mil to mm:
100 × 0.0254 = 2.54 mm
Real-world example — Plastic-film thickness
100 mils of plastic film equals 2.54 mm — useful when comparing US plastic-film catalogues (mils) to European supplier catalogues (mm) for the same product.
100 mil × 0.0254 = 2.54 mm
Real-world example — Single-mil to millimeter
1 mil equals 0.0254 mm — the standard sub-millimeter precision unit of US-spec materials. The conversion bridges American (mils) and international (mm) supplier datasheets for foils, coatings, and films.
1 mil × 0.0254 = 0.0254 mm
Real-world example — Sheet-metal gauge
10 mils of sheet-metal coating equals 0.254 mm. Coating-specification engineers translating US mil-scale paint thickness to mm-scale international supplier specs do this conversion at every cross-border QA step.
10 mil × 0.0254 = 0.254 mm
Mil to Millimeter conversion table
Standard reference values for converting mils to millimeters:
| Mil [mil] | Millimeter [mm] |
|---|---|
| 0.01 | 0.000254 |
| 0.1 | 0.00254 |
| 1 | 0.0254 |
| 2 | 0.0508 |
| 3 | 0.0762 |
| 4 | 0.1016 |
| 5 | 0.127 |
| 10 | 0.254 |
| 20 | 0.508 |
| 30 | 0.762 |
| 40 | 1.016 |
| 50 | 1.27 |
| 100 | 2.54 |
| 500 | 12.7 |
| 1000 | 25.4 |
Frequently asked questions
How many millimeters is 1 mil?
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How many millimeters is 100 mils?
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Metric / SI (7 units)
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Nautical (1 units)
Sources & references
Conversion factor (1 mil = 0.0254 mm) 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 Hydrographic Organization — Resolution on the Nautical Mile
International authority that standardised the nautical mile at exactly 1852 m in 1929 — the value adopted worldwide for sea and air navigation.