Convert Inches to MM (in to mm)
Convert inches to mm instantly. 1 in = 25.4 mm. Free inches-to-mm converter with table and formula.
This inches to mm converter gives you exact results as you type. One inch equals 25.4 millimeters (1 in = 25.4 mm). It works offline once loaded and never sends your data anywhere.
The inch has been defined as exactly 2.54 centimeters since the international agreement of 1959. Conversions like this one matter in distance and length measurements in engineering, construction, travel, and everyday use. It bridges the imperial/US customary system and the metric system, which is why this conversion comes up so often. Millimeters are the standard unit in engineering drawings and manufacturing tolerances.
0.02542.540000e-52.5425.41.578283e-50.0277780.0833331Conversion formula
millimeters = inches × 25.4Conversion table
| Value | Converted |
|---|---|
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 25 in | 635 mm |
| 50 in | 1,270 mm |
| 100 in | 2,540 mm |
Frequently Asked Questions
How many millimeters are in a inch?
1 in = 25.4 mm. So 10 inches equal 254 millimeters.
How do you convert inches to millimeters manually?
Multiply the number of inches by 25.4: millimeters = inches × 25.4. For example, 10 in × 25.4 = 254 mm.
Is the inches to mm conversion exact?
Yes — both units have exact definitions, so the conversion itself is exact. The factor 25.4 shown here is rounded for readability; the converter computes with full precision.
Is this inches to mm converter free and private?
Yes. It is completely free, requires no signup, and the conversion happens entirely in your browser — no values are sent to any server.
Related conversions
Need a different unit? Use the full Unit Converter for every supported unit and category.