Convert Mil to Microinch
Convert mils to microinches instantly. 1 mil = 1000 microinch — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Microinch 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".
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 to Microinch conversion formula
The relationship between mils and microinches:
To convert mils to microinches, multiply the value in mils by 1000. To reverse, multiply microinches by 0.001.
How to use this converter
Type a value into the calculator. The result in microinches updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Microinch to Mil converter for the reverse direction.
Step-by-step: convert mils to microinches
- Write down the value in mils (mil).
- Multiply that value by the factor 1000.
- The product is the equivalent value in microinches (µin).
- To reverse, multiply the microinch value by 0.001.
Worked examples
Example 1 — Convert 1 mil to µin:
1 × 1000 = 1000 µin
Example 2 — Convert 100 mil to µin:
100 × 1000 = 100000 µin
Real-world example — Infrared to visible-spectrum mapping
A 10-mil thermal infrared wavelength corresponds to a much larger number in microinches, the unit favoured for ultraviolet and visible-light specifications.
10 mil × 1000 = 10000 µin
Real-world example — Mid-micron to nanometer
3 mils equals 3,000 microinches — useful when relating mid-infrared wavelengths (typically quoted in microns) to nanometer-scale visible-light wavelength tables.
3 mil × 1000 = 3000 µin
Real-world example — From microns to sub-micron features
One mil equals one thousand microinches — the conversion semiconductor designers do constantly when comparing mask feature dimensions to actual transistor gate lengths.
1 mil × 1000 = 1000 µin
Mil to Microinch conversion table
Standard reference values for converting mils to microinches:
| Mil [mil] | Microinch [µin] |
|---|---|
| 0.01 | 10 |
| 0.1 | 100 |
| 1 | 1000 |
| 2 | 2000 |
| 3 | 3000 |
| 4 | 4000 |
| 5 | 5000 |
| 10 | 10000 |
| 20 | 20000 |
| 30 | 30000 |
| 40 | 40000 |
| 50 | 50000 |
| 100 | 100000 |
| 500 | 500000.0000000001 |
| 1000 | 1000000.0000000001 |
Frequently asked questions
How many microinches is 1 mil?
How do I convert mils to microinches?
How do I convert microinches back to mils?
How many microinches is 100 mils?
Popular length unit conversions
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Metric / SI (7 units)
Imperial / US Customary (26 units)
Nautical (1 units)
Sources & references
Conversion factor (1 mil = 1000 µin) 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.