Convert length units instantly — meters, feet, inches, centimeters, kilometers, miles, and more.
| Unit | Name | Value |
|---|---|---|
| m | Meter | 0.0254 |
| km | Kilometer | 0.0000254 |
| cm | Centimeter | 2.54 |
| mm | Millimeter | 25.4 |
| ft | Foot | 0.083333333 |
| yd | Yard | 0.027777778 |
| mi | Mile | 0.000015782828 |
| nmi | Nautical Mile | 0.000013714903 |
Multiply the number of Inchs by 25.4 to get Millimeters. Formula: mm = in × 25.4. Example: 10 in × 25.4 = 254 mm. To reverse, divide Millimeters by 25.4 to get Inchs.
| Inch (in) | Millimeter (mm) |
|---|---|
| 0.001 in | 0.0254 mm |
| 0.01 in | 0.254 mm |
| 0.1 in | 2.54 mm |
| 0.5 in | 12.7 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 20 in | 508 mm |
| 50 in | 1270 mm |
| 100 in | 2540 mm |
| 250 in | 6350 mm |
| 500 in | 12700 mm |
| 1000 in | 25400 mm |
| 10000 in | 254000 mm |
To convert Inch to Millimeter, multiply by 25.4. Example: 10 in = 254 mm
To convert Millimeter back to Inch, divide by 25.4 (multiply by 0.0393701). Use the swap button above.
Start with 100 Inchs = 2540 mm as your reference point. Scale up or down from there.
1 inch = 25.4 mm exactly — one of the most important conversion factors in all of engineering. Every US engineer working with metric partners, ISO standards, or international supply chains performs this conversion multiple times daily.
CNC machines in the US often work in inches while ISO tolerancing standards use millimetres. Machinists convert between the two for every part programmed to inch dimensions that must meet metric tolerance specifications.
US medical device drawings use inches while FDA and EU MDR submissions require millimetres. Every medical device engineer converts inch dimensions to millimetres for regulatory documentation and international market access.
US standard fasteners (bolts, screws, nuts) use inch dimensions while metric fasteners use millimetres. Engineers and buyers selecting the right fastener convert between inches and millimetres for every hardware specification.
Display panel pixel pitch is specified in millimetres while screen diagonal size uses inches. Display engineers convert between inches and millimetres for every panel specification, viewing angle calculation, and PPI computation.
US pipe sizes are nominal inch dimensions while thread specifications and fitting tolerances use millimetres. Plumbers working with mixed US and metric systems convert between inches and millimetres for every cross-system connection.
The Inch is a unit of Length measurement (symbol: in). 1 in = 25.4 mm. Used in scientific and practical Length measurement applications.
The Millimeter is a unit of Length measurement (symbol: mm). It is part of an internationally recognised measurement system used alongside the Inch.
The inch has one of the most colourful origin stories in measurement history. An English statute from 1324 under King Edward II defined it as 'three grains of barley, dry and round, placed end to end'. Before that, it was often defined as the width of a thumb — hence the word in many languages (French: 'pouce', Dutch: 'duim', both meaning thumb). The inch was standardised at exactly 25.4 mm in 1959 under the International Yard and Pound Agreement signed by the US, UK, Canada, Australia, and South Africa. It remains dominant in the US and is universally used for screen sizes globally.
The millimetre was introduced alongside the metre in 1795 — one-thousandth of a metre. Its practical value emerged in precision engineering during the Industrial Revolution. By the 20th century, ISO engineering drawing standards adopted millimetres as the primary unit for all technical drawings worldwide. Today millimetres are the universal language of engineering — from watch mechanisms to aircraft fuselages.
Common use: Inch to Millimeter conversion is needed when working with international standards, scientific publications, or reference materials that use different unit systems for Length measurement.