Convert Millimeter to Microinch
Convert millimeters to microinches instantly. 1 millimeter = 39370.0787401575 microinch — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Microinch 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.
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.
Millimeter to Microinch conversion formula
The relationship between millimeters and microinches:
To convert millimeters to microinches, multiply the value in millimeters by 39370.0787401575. To reverse, multiply microinches by 2.54e-5.
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 Millimeter converter for the reverse direction.
Step-by-step: convert millimeters to microinches
- Write down the value in millimeters (mm).
- Multiply that value by the factor 39370.0787401575.
- The product is the equivalent value in microinches (µin).
- To reverse, multiply the microinch value by 2.54e-5.
Worked examples
Example 1 — Convert 1 mm to µin:
1 × 39370.0787401575 = 39370.0787401575 µin
Example 2 — Convert 100 mm to µin:
100 × 39370.0787401575 = 3937007.8740157485 µin
Real-world example — Centimeter to wavelength scale
One millimeter equals 10 million microinches. Physics curricula use this kind of conversion to relate everyday measurements to atomic and optical scales.
1 mm × 39370.0787401575 = 39370.0787401575 µin
Real-world example — Small-scale to atomic-scale
One millimeter equals 10 million microinches — useful for physics curricula that relate everyday measurements to atomic and optical scales.
1 mm × 39370.0787401575 = 39370.0787401575 µin
Millimeter to Microinch conversion table
Standard reference values for converting millimeters to microinches:
| Millimeter [mm] | Microinch [µin] |
|---|---|
| 0.01 | 393.7007874016 |
| 0.1 | 3937.0078740157 |
| 1 | 39370.0787401575 |
| 2 | 78740.157480315 |
| 3 | 118110.2362204725 |
| 4 | 157480.3149606299 |
| 5 | 196850.3937007874 |
| 10 | 393700.7874015748 |
| 20 | 787401.5748031497 |
| 30 | 1181102.3622047245 |
| 40 | 1574803.1496062994 |
| 50 | 1968503.9370078743 |
| 100 | 3937007.8740157485 |
| 500 | 1.968504e+7 |
| 1000 | 3.937008e+7 |
Frequently asked questions
How many microinches is 1 millimeter?
How do I convert millimeters to microinches?
How do I convert microinches back to millimeters?
How many microinches is 100 millimeters?
Popular length unit conversions
Convert Millimeter to other length units
Show all Millimeter conversions
Metric / SI (17 units)
Imperial / US Customary (27 units)
Nautical (1 units)
Astronomical (9 units)
Atomic / Physics (6 units)
Typographic (3 units)
Sources & references
Conversion factor (1 mm = 39370.0787401575 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 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.