Convert Millimeter (mm) (mm) to Inch (in) (in)
Category: Length
1 mm = 0.03937 in
High-precision rounding: 6 decimals
How to convert millimeter (mm) to inch (in)
We convert by pivoting through the SI base unit for Length and applying exact factors where applicable.
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Examples
Linear unit conversions use standardized factors; many are exact by definition (e.g., 1 in = 25.4 mm, 1 ft = 0.3048 m).
Common mistakes
- Confusing international foot (0.3048 m) with legacy ‘US survey foot’ in old datasets.
- Rounding mid-calculation; keep precision to the end.
About Length
Length measures distance or size. In SI it derives from the meter, defined via the speed of light, which ensures exact, reproducible conversions. Typical applications include construction, mapping, manufacturing tolerances, and navigation; legacy units like inches and feet remain common in trade and building plans.
About Millimeter (mm)
Millimeter (mm)
Equals 1/1000 of a meter. Used for tolerances, mechanical parts, PCB traces, and rainfall amounts. Ideal when sub-centimeter precision is required.
History: Adopted alongside other metric submultiples; machine tooling and metrology standardized on millimeters to simplify interchangeability.
About Inch (in)
Inch (in)
Imperial/US unit exactly defined as 25.4 mm. Still widespread in hardware, displays (screen size), and woodworking. Conversions to/from SI are exact thanks to the 1959 agreement.
History: Various historic definitions existed; international inch was fixed at exactly 25.4 mm in 1959 by US, UK and Commonwealth countries to harmonize trade.