Convert Microinch to Mil
Convert microinches to mils instantly. 1 microinch = 0.001 mil — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Mil to Microinch converter for the reverse conversion.
Units explained
Microinch
A microinch is an Imperial unit of length equal to one millionth of an inch (2.54×10⁻⁸ m). It is used almost exclusively in surface-finish specifications for precision machining and optical components.
The microinch is derived from the inch using the SI-style prefix micro- to denote one millionth. Standardised through the 1959 International Yard and Pound Agreement, which fixed the inch at exactly 25.4 mm.
Microinches express surface roughness (Ra values) in US-based precision manufacturing — typical machined surfaces are 16–125 µin. Optical components and bearing races are often specified to 1–4 µin Ra.
Used in US precision-manufacturing literature throughout the 20th century; value became exact in 1959 when the inch was fixed at 25.4 mm via the International Yard and Pound Agreement.
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".
Microinch to Mil conversion formula
The relationship between microinches and mils:
To convert microinches to mils, multiply the value in microinches by 0.001. To reverse, multiply mils by 1000.
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 Microinch converter for the reverse direction.
Step-by-step: convert microinches to mils
- Write down the value in microinches (µin).
- Multiply that value by the factor 0.001.
- The product is the equivalent value in mils (mil).
- To reverse, multiply the mil value by 1000.
Worked examples
Example 1 — Convert 1 µin to mil:
1 × 0.001 = 0.001 mil
Example 2 — Convert 100 µin to mil:
100 × 0.001 = 0.1 mil
Real-world example — Sub-visible-light wavelength
500 microinches (the green-yellow visible band) equals 0.5 mils — the canonical conversion in optics between wavelength specifications and micron-scale lens-coating thicknesses.
500 µin × 0.001 = 0.5 mil
Real-world example — Spanning sub-micron to micron scale
Crossing from microinches to mils is the everyday workflow of microscopy and semiconductor engineering — a measurement of 1000 microinches translates to a much more compact value in mils that fits the scale of biological cells and process nodes.
1000 µin × 0.001 = 1 mil
Microinch to Mil conversion table
Standard reference values for converting microinches to mils:
| Microinch [µin] | Mil [mil] |
|---|---|
| 0.01 | 1e-5 |
| 0.1 | 0.0001 |
| 1 | 0.001 |
| 2 | 0.002 |
| 3 | 0.003 |
| 4 | 0.004 |
| 5 | 0.005 |
| 10 | 0.01 |
| 20 | 0.02 |
| 30 | 0.03 |
| 40 | 0.04 |
| 50 | 0.05 |
| 100 | 0.1 |
| 500 | 0.5 |
| 1000 | 1 |
Frequently asked questions
How many mils is 1 microinch?
How do I convert microinches to mils?
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How many mils is 100 microinches?
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Sources & references
Conversion factor (1 µin = 0.001 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.