Millimetres to Inches — Technical Conversions Made Easy
Millimetres (mm) are a fundamental unit in engineering, manufacturing, and construction. Because 1 inch is defined as exactly 25.4 mm, the conversion to inches is: divide by 25.4. This is an exact, internationally recognised definition.
Millimetre-to-inch conversions are common in hardware and tooling. European and Asian tools are often specified in metric, while North American equivalents use inches. Tyre widths, bolt diameters, and camera sensor sizes are typical examples where both units appear side by side.
Common references: 10 mm = 0.394 in; 25.4 mm = 1 in (exact); 50 mm = 1.969 in; 100 mm = 3.937 in; 300 mm = 11.811 in; 1000 mm = 39.37 in.
Formula
To convert millimetres to inches: inches = mm × 0.0393701. To get centimetres: cm = mm ÷ 10. To get feet: ft = inches ÷ 12.
Common Millimetres to Inches Conversions
- 1 mm = 0.039 inches
- 5 mm = 0.197 inches
- 10 mm = 0.394 inches
- 25 mm ≈ 0.984 inches
- 25.4 mm = 1 inch (exact)
- 50 mm = 1.969 inches
- 100 mm = 3.937 inches
- 300 mm = 11.811 inches
Practical Applications
- Tyre sizing — tyre widths (e.g. 205 mm) are in metric, but rim diameters are in inches
- Photography — lens focal lengths in mm, but film and sensor sizes often in inches
- Screen sizes — often marketed in inches; knowing the mm equivalent helps with technical specs
- Woodworking and joinery — combining metric sheet goods with imperial timber dimensions
- Medical devices — wound dressings, catheter sizes, and surgical instruments often use both
Related Calculators
- Inches to Millimetres — Convert inches to mm and cm.
- Centimetres to Inches — Convert cm to inches and feet.
- Inches to Centimetres — Convert inches to cm and mm.