Length / mm → in
Convert Millimeters to Inches
From a small measurement to a long distance. Move between metric and imperial units. Convert Millimeters (mm) to Inches (in). Find the formula, worked examples, unit definitions, and practical guidance below.
Reverse: Inches to Millimeters →
How to convert millimeters to inches
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 mm, b for the intermediate value in m, and y for the result in in.
in = mm × 0.001 ÷ 0.0254
Worked examples
10 mm ≈ 0.393700787402 in
Step 1: (10 × 0.001) ≈ 0.01 m.
Step 2: 0.01 ÷ 0.0254 ≈ 0.393700787402 in.20 mm ≈ 0.787401574803 in
Step 1: (20 × 0.001) ≈ 0.02 m.
Step 2: 0.02 ÷ 0.0254 ≈ 0.787401574803 in.
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 Millimeters
A millimeter is one thousandth of a meter. Small dimensions and engineering drawings often use millimeters; retain the precision of the original measurement.
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.
Definitions and sources
Use consistent length units when carrying dimensions into construction calculations.
Millimeters to inches reference table
| Millimeters (mm) | Inches (in) |
|---|---|
| 1 | 0.0393700787402 |
| 5 | 0.196850393701 |
| 10 | 0.393700787402 |
| 25 | 0.984251968504 |
| 50 | 1.96850393701 |
| 100 | 3.93700787402 |
| 1000 | 39.3700787402 |
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