Convert Inch (in) to Millimeter (mm)
Category: Length
1 in = 25.4 mm
Precision: 6 decimals; very small non-zero results use significant digits.
How to convert inch (in) to millimeter (mm)
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.
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Quick conversion table
Handy values for Inch (in) to Millimeter (mm). Click a value to calculate that result.
| Inch (in) | Millimeter (mm) |
|---|---|
| 25.4 | |
| 12.7 | |
| 63.5 | |
| 254 |
Conversion formula
Use the following formula:
Millimeter (mm) ≈ Inch (in) × 25.4
Convert length from Inch (in) to Millimeter (mm) using a fixed unit ratio. Round only the final result.
Common mistakes
- Confusing international foot (0.3048 m) with legacy ‘US survey foot’ in old datasets.
- Rounding mid-calculation; keep precision to the end.
Unit facts
- Inch (in): The inch is exactly 25.4 millimeters (since 1959). Historically based on a thumb’s width; standardized for engineering and trade.
- Millimeter (mm): A millimeter is 1/1000 of a meter; used in machining and precision engineering.
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.
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.