Inches to Millimeters (in to mm) Converter
1 Inch equals 25.4 Millimeters (1 in = 25.4 mm). Convert Inches to Millimeters with formula, table, and examples.
One inch equals exactly 25.4 millimeters. This precise, exact conversion is one of the most important in engineering and manufacturing, forming the bridge between imperial and metric precision measurement. Every workshop, factory, and design office that handles both systems relies on this relationship daily.
How to Convert Inches to Millimeters
- Take your value in Inches
- Multiply by 25.4
- Read the result in Millimeters
Common Inches to Millimeters Conversions
| Inches (in) | Millimeters (mm) | Status |
|---|---|---|
| 0.25 in | 6.35 mm | |
| 0.5 in | 12.7 mm | |
| 1 in | 25.4 mm | |
| 2 in | 50.8 mm | |
| 3 in | 76.2 mm | |
| 4 in | 101.6 mm | |
| 5 in | 127 mm | |
| 6 in | 152.4 mm | |
| 8 in | 203.2 mm | |
| 10 in | 254 mm | |
| 12 in | 304.8 mm | |
| 18 in | 457.2 mm | |
| 24 in | 609.6 mm | |
| 36 in | 914.4 mm | |
| 48 in | 1,219.2 mm | |
| 72 in | 1,828.8 mm | |
| 100 in | 2,540 mm |
Good to Know About Inches to Millimeters Conversion
The relationship 1 inch = 25.4 mm is the single most important bridge between imperial and metric systems. Every other imperial-to-metric length conversion derives from this one definition.
Inches to Millimeters: What You Need to Know
A 1/4-inch drill bit is exactly 6.35 mm. Pipe fittings labeled in inches need conversion to millimeters for metric plumbing systems. CNC machining programs may specify dimensions in either unit. The 25.4 mm/inch relationship is so fundamental that it was the basis for the 1959 International Yard and Pound Agreement that standardized all imperial length units.
What is a Inch? in
An imperial unit of length equal to exactly 2.54 centimeters. Commonly used in the US and UK for screen sizes, body measurements, and construction.
Learn more about Inch →What is a Millimeter? mm
A metric unit of length equal to one thousandth of a meter. Used in engineering, manufacturing, and precise measurements.
Learn more about Millimeter →Going the other way? Use our Millimeters to Inches converter.
Inches to Millimeters FAQ
-
One inch equals exactly 25.4 millimeters. This is an exact definition, not an approximation. It was established by international agreement in 1959.
-
Multiply the number of inches by 25.4. For example, 3 inches × 25.4 = 76.2 mm. For fractions, convert to decimals first: 3/8 inch = 0.375 × 25.4 = 9.525 mm.
-
1/2 inch equals exactly 12.7 millimeters. Common fractional conversions: 1/4" = 6.35 mm, 3/8" = 9.525 mm, 1/2" = 12.7 mm, 3/4" = 19.05 mm, 1" = 25.4 mm.
Non-Frequently Asked Questions About Inches to Millimeters
Questions nobody should ask - but someone did.
-
Because inches evolved from barleycorns and thumbs, while millimeters evolved from the meter (which was based on the Earth's circumference). When two measurement systems derived from completely different starting points finally meet, the conversion factor is whatever number the math produces. 25.4 is not ugly - it is honest.
Related Articles About Inches to Millimeters
Need the reverse? Use our Millimeters to Inches converter. See all Length & Distance converters.