Length / in → mm
Convert Inches to Millimeters
From a small measurement to a long distance. Move between metric and imperial units. Convert Inches (in) to Millimeters (mm). Find the formula, worked examples, unit definitions, and practical guidance below.
Reverse: Millimeters to Inches →
How to convert inches to millimeters
Length conversion changes the unit of a distance. Area and volume need squared and cubed factors; this calculator does not convert square feet or cubic feet.
Use x for the value in in, b for the intermediate value in m, and y for the result in mm.
mm = in × 0.0254 ÷ 0.001
Worked examples
10 in ≈ 254 mm
Step 1: (10 × 0.0254) ≈ 0.254 m.
Step 2: 0.254 ÷ 0.001 ≈ 254 mm.20 in ≈ 508 mm
Step 1: (20 × 0.0254) ≈ 0.508 m.
Step 2: 0.508 ÷ 0.001 ≈ 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 Inches
The international inch is exactly 0.0254 meters. Screen sizes usually describe a diagonal length in inches, not the width of a display.
About Millimeters
A millimeter is one thousandth of a meter. Small dimensions and engineering drawings often use millimeters; retain the precision of the original measurement.
Definitions and sources
Use consistent length units when carrying dimensions into construction calculations.
Inches to millimeters reference table
| Inches (in) | Millimeters (mm) |
|---|---|
| 1 | 25.4 |
| 5 | 127 |
| 10 | 254 |
| 25 | 635 |
| 50 | 1270 |
| 100 | 2540 |
| 1000 | 25400 |
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