Unit Converter / Inches to Millimeters
Inches to Millimeters Converter
1 inch = 25.4 millimeters at 96 DPI, the CSS reference resolution. To convert, multiplyinches by 25.4: in × 25.4 = mm. Change the DPI below for print and image work, where a pixel is whatever the output resolution says it is.
Inches to Millimeters table
Standard values at 96 DPI.
| Inches (in) | Millimeters (mm) |
|---|---|
| 0.25 | 6.35 |
| 0.5 | 12.7 |
| 1 | 25.4 |
| 2 | 50.8 |
| 3 | 76.2 |
| 4 | 101.6 |
| 6 | 152.4 |
| 8.5 | 215.9 |
| 11 | 279.4 |
| 12 | 304.8 |
| 24 | 609.6 |
How the conversion works
The US print unit: US Letter is 8.5 by 11 inches, and print layouts are still specced in inches across North America. The fine metric unit: print tolerances, paper (A4 is 210 by 297 mm) and CSS print stylesheets use millimeters. Exactly 25.4 mm make an inch. The CSS specification anchors the whole system to the inch: at the reference resolution of 96 DPI, one inch is exactly 96 pixels, one point is 96/72 pixels, and the metric units follow from the inch being exactly 25.4 millimeters. Converting inches to millimeters therefore goes through that anchor: inches to pixels, then pixels to millimeters. For example,4 in = 101.6 mm.
The DPI setting matters only when pixels meet the physical world. On screen, CSS pixels are defined by the 96 DPI reference and the conversion above is exact. In a 300 DPI print file or image, an inch holds 300 pixels instead, so the same measurement converts differently; set the resolution to match the file you are working with.