Convert Mil to Micrometer
Convert mils to micrometers instantly. 1 mil = 25.4 micrometer — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Micrometer 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".
Micrometer
A micrometer (also called a micron) is a metric unit of length equal to one millionth of a meter (1×10⁻⁶ m). It is the standard unit for measuring microscopic dimensions in biology, materials science, and semiconductor manufacturing.
Defined alongside the meter when France adopted the metric system in 1795, using the SI prefix micro- (from Greek mikros, "small") to denote one-millionth.
Micrometers are used to measure cell sizes, bacteria, semiconductor process nodes, fiber diameters, dust particles, and wavelengths of infrared radiation. The diameter of a human hair is about 70 μm.
Defined in 1795 as part of the original French metric system; the name "micron" was officially deprecated by the BIPM in 1967 in favor of micrometer.
Mil to Micrometer conversion formula
The relationship between mils and micrometers:
To convert mils to micrometers, multiply the value in mils by 25.4. To reverse, multiply micrometers by 0.0393700787.
How to use this converter
Type a value into the calculator. The result in micrometers updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Micrometer to Mil converter for the reverse direction.
Step-by-step: convert mils to micrometers
- Write down the value in mils (mil).
- Multiply that value by the factor 25.4.
- The product is the equivalent value in micrometers (μm).
- To reverse, multiply the micrometer value by 0.0393700787.
Worked examples
Example 1 — Convert 1 mil to μm:
1 × 25.4 = 25.4 μm
Example 2 — Convert 100 mil to μm:
100 × 25.4 = 2540 μm
Real-world example — Paper and film thicknesses
At the thickness of office paper (roughly 3 mils), converting between sub-millimeter units is routine for packaging and printing buyers comparing quotes from metric and US suppliers.
3 mil × 25.4 = 76.2 μm
Real-world example — Plastic-film thickness alternates
A 150-mil plastic film converts cleanly to micrometers — useful for packaging buyers reconciling supplier datasheets across metric and US measurement systems.
150 mil × 25.4 = 3810 μm
Real-world example — Hair-width scale measurements
A 70-mil measurement (about the diameter of a human hair) is the kind of value materials engineers regularly express in adjacent micro-scale units like micrometers for direct comparison across supplier datasheets.
70 mil × 25.4 = 1778 μm
Mil to Micrometer conversion table
Standard reference values for converting mils to micrometers:
| Mil [mil] | Micrometer [μm] |
|---|---|
| 0.01 | 0.254 |
| 0.1 | 2.54 |
| 1 | 25.4 |
| 2 | 50.8 |
| 3 | 76.2 |
| 4 | 101.6 |
| 5 | 127 |
| 10 | 254 |
| 20 | 508 |
| 30 | 762 |
| 40 | 1016 |
| 50 | 1270 |
| 100 | 2540 |
| 500 | 12700 |
| 1000 | 25400 |
Frequently asked questions
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Metric / SI (7 units)
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Sources & references
Conversion factor (1 mil = 25.4 μm) 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.