Inch to Millimeter Converter
Convert Inch (in) to Millimeter (mm) instantly. 1 in = 25.4 mm.
Length Converter
31 units available
1 in = 25.4 mm
Formula:
mm = in × 25.4With your value: 1 in = 25.4 mm
How big is that?
Everyday references on a logarithmic scale, all expressed in inch so you can sanity-check the result.
Other Inch to Millimeter conversions
Inch to Millimeter Conversion Table
| Inch (in) | Millimeter (mm) |
|---|---|
| 0.5 | 12.7 |
| 1 | 25.4 |
| 2 | 50.8 |
| 5 | 127 |
| 10 | 254 |
| 15 | 381 |
| 20 | 508 |
| 25 | 635 |
| 50 | 1,270 |
| 100 | 2,540 |
| 250 | 6,350 |
| 500 | 12,700 |
| 1000 | 25,400 |
Millimeter to Inch Conversion Table
| Millimeter (mm) | Inch (in) |
|---|---|
| 0.5 | 0.019685 |
| 1 | 0.03937 |
| 2 | 0.07874 |
| 5 | 0.19685 |
| 10 | 0.393701 |
| 15 | 0.590551 |
| 20 | 0.787402 |
| 25 | 0.984252 |
| 50 | 1.968504 |
| 100 | 3.937008 |
| 250 | 9.84252 |
| 500 | 19.685039 |
| 1000 | 39.370079 |
Where these values come from
Every factor on this page is traced to the document that defines it. See the full provenance dataset or our methodology.
Inch (in)
Length
1 inch = 25.4 mm exactly, fixed by the 1959 international yard and pound agreement.
Source: International Yard and Pound Agreement of 1959; NIST Federal Register Notice 59-5442
US, UK, Canada, Australia, New Zealand, South Africa · Reviewed 2026-07-01
Millimeter (mm)
Length
Traceable to the metre, defined by fixing the speed of light in vacuum at 299 792 458 m/s. Imperial lengths derive from the 1959 international yard (0.9144 m exactly).
Source: BIPM, The International System of Units (SI), 9th edition, 2019 (updated 2024)
Bureau International des Poids et Mesures · Reviewed 2026-07-01
How to Convert Inch to Millimeter
To convert from Inch (in) to Millimeter (mm), multiply the value by 25.4.
Formula: mm = in × 25.4
Reverse: in = mm × 0.0393700787
Step-by-Step Example
- Start with your value in Inch. For example: 5 in
- Multiply by the conversion factor: 5 x 25.4
- The result is: 127 mm
About Inch
The inch is an imperial unit equal to 1/12 of a foot or 2.54 centimeters. It is widely used in the US and UK for small measurements.
Fun Fact: The inch was historically defined as the width of a man's thumb.
Common uses: screen sizes, construction, clothing.
About Millimeter
The millimeter equals one thousandth of a meter and is used for precise measurements in engineering and manufacturing.
Common uses: engineering, rainfall measurement, manufacturing.
Frequently Asked Questions
How many Millimeter are in 1 Inch?
There are exactly 25.4 Millimeter in 1 Inch. This means the conversion factor from Inch to Millimeter is 25.4.
What is the formula to convert Inch to Millimeter?
The formula to convert Inch to Millimeter is: mm = in × 25.4. For example, to convert 10 Inch to Millimeter, you would multiply 10 by 25.4.
What is a Inch?
The inch is an imperial unit equal to 1/12 of a foot or 2.54 centimeters. It is widely used in the US and UK for small measurements.
What is a Millimeter?
The millimeter equals one thousandth of a meter and is used for precise measurements in engineering and manufacturing.
What are the common uses of Inch?
The Inch is commonly used in screen sizes, construction, clothing.
Related Length Conversions
Cite this page
UnitConvertLab. (2026). Inch to Millimeter converter. UnitConvertLab. Retrieved from https://unitconvertlab.com/convert/inch-to-millimeter