Inches to Millimetres — Precision Conversion
The millimetre (mm) is a metric unit equal to one thousandth of a metre, commonly used in engineering, manufacturing, and technical drawings. The inch is defined as exactly 25.4 millimetres — this is an exact definition established in 1959, making all inch-to-millimetre conversions perfectly precise.
This conversion is particularly important in engineering and manufacturing contexts where precise measurements are critical. Drill bit sizes, screw diameters, pipe fittings, and mechanical tolerances are often specified in both inches and millimetres depending on the country of manufacture.
Common references: 1/4 in = 6.35 mm; 1/2 in = 12.7 mm; 1 in = 25.4 mm; 2 in = 50.8 mm; 6 in = 152.4 mm; 12 in = 304.8 mm.
Formula
To convert inches to millimetres: mm = inches × 25.4 (exact). To get centimetres: cm = inches × 2.54.
Common Inches to Millimetres Conversions
- 1/16 inch = 1.588 mm
- 1/8 inch = 3.175 mm
- 1/4 inch = 6.35 mm
- 1/2 inch = 12.7 mm
- 1 inch = 25.4 mm
- 2 inches = 50.8 mm
- 6 inches = 152.4 mm
- 12 inches (1 foot) = 304.8 mm
Where This Conversion Is Used
- Engineering and machining — tolerances and dimensions on technical drawings often mix inch and metric units
- DIY and woodworking — timber, screws, and fixings may be sold in either system
- Plumbing — pipe diameters are frequently quoted in inches even in metric countries
- Photography — sensor and print sizes are often given in inches
- Electronics — screen sizes and PCB dimensions are commonly in inches
Related Calculators
- Millimetres to Inches — Convert mm to inches and cm.
- Centimetres to Inches — Convert cm to inches and feet.
- Inches to Centimetres — Convert inches to cm and mm.