Inches to millimetres
Multiply inches by 25.4 to get millimetres.
3 in = 76.2 mm
How to convert inches to millimetres
The millimetre is one thousandth of a metre (10⁻³ m). The inch is exactly 2.54 centimetres (0.0254 m), by the 1959 international agreement.
Worked example — 3 in: 3 × 25.4 = 76.2 mm.
Inches to millimetres table
| Inches | Millimetres |
|---|---|
| 0.25 in | 6.35 mm |
| 0.5 in | 12.7 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 6 in | 152.4 mm |
| 10 in | 254 mm |
| 12 in | 304.8 mm |
| 24 in | 609.6 mm |
Reverse and related
About inches and millimetres
Inch (in)
1 in = 25.4 mmDefinition. Exactly 2.54 centimetres (0.0254 m), by the 1959 international agreement
History and origin
The inch takes its name from the Latin uncia, a twelfth part, and has always been one twelfth of a foot. The 1959 agreement fixed it at exactly 2.54 centimetres.
Current use
Inches are used for screen and TV sizes worldwide, and in the United States for height, lumber and hardware.
Source: International Yard and Pound Agreement (1959); NIST Handbook 44, App. C
Millimetre (mm)
1 mm = 0.0393701 inDefinition. One thousandth of a metre (10⁻³ m)
History and origin
The millimetre is one thousandth of a metre, defined with the rest of the decimal metric system in the 1790s. Its small size suits precise work.
Current use
Millimetres are used for rainfall, engineering tolerances, and the sizes of screws, hardware and printed parts.
Source: BIPM, The International System of Units (SI), 9th ed. (2019)
Where people use this
Inches: screen sizes, height, lumber and hardware. Millimetres: rainfall, engineering tolerances, screws and hardware. 1 inch is exactly 25.4 mm.
Every value is carried to full double precision; the display is rounded.
Sources: BIPM, The International System of Units (SI), 9th ed. (2019); International Yard and Pound Agreement (1959); NIST Handbook 44, App. C.
Questions people ask
How many mm is 1 inch?
One inch is exactly 25.4 mm. To convert inches to mm, multiply by 25.4.
How many mm is half an inch?
Half an inch is 12.7 mm, and a quarter inch is 6.35 mm.
What is 2 inches in mm?
2 inches is 50.8 mm, and 3 inches is 76.2 mm.