Convert millimetres to inches and inches to millimetres
Millimetres and inches coexist throughout UK engineering, construction, and DIY. While metric measurements dominate modern specifications, imperial inches persist in older building stock, American-sourced components, and traditional trades. Pipe fittings, drill bits, bolt sizes, and timber dimensions frequently need translating between the two systems. The relationship is exact: one inch equals precisely 25.4 millimetres. This definition, established in 1959, means that conversions between mm and inches introduce no rounding error at the fundamental level. In practice, you divide millimetres by 25.4 to get inches, or multiply inches by 25.4 to get millimetres. This converter also shows the nearest fractional inch, which is invaluable for workshop use. Engineers and tradespeople often work in fractions (halves, quarters, eighths, sixteenths) rather than decimals, so knowing that 12.7 mm is exactly half an inch saves time and prevents measurement errors.
To use the millimetres to inches converter: 1. Select the conversion direction. Choose "Millimetres to Inches" if you have a metric measurement. Choose "Inches to Millimetres" for the reverse. 2. For mm to inches: Enter the millimetre value. The converter shows decimal inches, the nearest fractional inch, and centimetres. 3. For inches to mm: Enter the inch value (can be decimal). The converter shows millimetres, centimetres, and the nearest fraction. 4. Results update instantly, letting you quickly look up multiple sizes in succession.
The conversion uses the exact definition: 1 inch = 25.4 mm. Millimetres to Inches: Inches = mm / 25.4 Centimetres = mm / 10 Example: 50 mm = 50 / 25.4 = 1.9685 inches (approximately 2 inches or 1 31/32") Inches to Millimetres: mm = inches x 25.4 Centimetres = mm / 10 Example: 3/4 inch = 0.75 x 25.4 = 19.05 mm The fractional inch display rounds to the nearest 16th of an inch, which is the standard precision for most workshop applications.
Inputs: Millimetres: 8. Direction: mm to inches.
Inputs: Inches: 0.75. Direction: inches to mm.
Inputs: Millimetres: 18. Direction: mm to inches.
Common workshop conversions: 1/8" = 3.175 mm, 1/4" = 6.35 mm, 3/8" = 9.525 mm, 1/2" = 12.7 mm, 5/8" = 15.875 mm, 3/4" = 19.05 mm, 7/8" = 22.225 mm, 1" = 25.4 mm. UK plumbing nominal sizes: "half inch" pipe = 15 mm, "three quarter inch" = 22 mm, "one inch" = 28 mm. Standard UK timber thicknesses include 12 mm, 18 mm, and 25 mm (roughly 1/2", 3/4", and 1").