Typography / in → mm
Convert CSS inches to Millimeters
Convert absolute CSS lengths and desktop-publishing points. Convert CSS inches (in) to Millimeters (mm). Find the formula, worked examples, unit definitions, and practical guidance below.
Reverse: Millimeters to CSS inches →
How to convert CSS inches to millimeters
These use CSS definitions: 1 inch = 96 CSS pixels = 72 points = 6 picas. A CSS pixel is not a physical screen pixel. Relative em, rem, and viewport units need a rendering context and are excluded.
Use x for the value in in, b for the intermediate value in in, and y for the result in mm.
mm = in ÷ 0.03937007874015748
Worked examples
10 in ≈ 254 mm
Step 1: (10 × 1) ≈ 10 in.
Step 2: 10 ÷ 0.0393700787402 ≈ 254 mm.20 in ≈ 508 mm
Step 1: (20 × 1) ≈ 20 in.
Step 2: 20 ÷ 0.0393700787402 ≈ 508 mm.
Results are rounded to 12 significant digits. Converting units does not increase the precision of the original measurement. Very large or small values outside JavaScript’s finite numeric range are rejected.
About CSS inches
CSS inches (in) measures typography under the conventions above. The base value in in is (x × 1), where x is the numerical value in in. Factors shown here are rounded for display; calculations use the stored factor.
About Millimeters
Millimeters (mm) measures typography under the conventions above. The base value in in is (x × 0.0393700787402), where x is the numerical value in mm. Factors shown here are rounded for display; calculations use the stored factor.
Definitions and sources
Keep these unit conventions consistent when using measurements in construction calculations.
CSS inches to millimeters reference table
| CSS inches (in) | Millimeters (mm) |
|---|---|
| 1 | 25.4 |
| 5 | 127 |
| 10 | 254 |
| 25 | 635 |
| 50 | 1270 |
| 100 | 2540 |
| 1000 | 25400 |
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