Convert Inch to Millimeter (in → mm)
The inch is the global standard for screen sizes, pipe diameters, and shoe sizing in Anglo-Saxon countries.
Inch to Millimeter Conversion Table
10 common values| Inch | Millimeter |
|---|---|
| 1 in | 25.4 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 25 in | 635 mm |
| 50 in | 1,270 mm |
| 100 in | 2,540 mm |
| 250 in | 6,350 mm |
| 500 in | 12,700 mm |
| 1,000 in | 25,400 mm |
| 5,000 in | 127,000 mm |
How to Convert Inch to Millimeter Manually
Step by StepConverting inches to millimeters is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.
- 1Take your value in inchesStart with the number of inches (in) you want to convert.
- 2Multiply by 25.4The conversion factor from in to mm is 25.4. Multiply your value by this number.
- 3Read the result in millimetersThe result is your value in millimeters (mm).
Formula
Multiply the value in inches by 25.4. For the reverse direction, multiply by 0.03937.
mm = in × 25.4in = mm × 0.03937Tips
Use these in everyday conversions- 1 inch = 2.54 cm exactly by international agreement — no rounding.
- Screen sizes are always diagonal, never width. A 27-inch monitor is about 60 cm wide.
- To convert cm to inches mentally, divide by 2.5 and subtract 1.6%.
Common Mistakes
Avoid these- Reading a screen size as width. A 65-inch TV is about 143 cm wide — the 165 cm figure is diagonal.
- Using 2.5 instead of 2.54 on precision drawings — the 1.6% error matters in manufacturing.
- Confusing inches of length with inches of mercury (inHg) — a pressure unit, not length.
About Inch and Millimeter
What is the Inch?
The inch equals exactly 25.4 millimeters under the 1959 international yard and pound agreement. The word derives from the Old English 'ynce,' from Latin 'uncia' meaning one twelfth (the inch is one twelfth of a foot). Originally based on the width of a thumb, the inch has been standardized for centuries. It is the global standard for screen sizes (a 15-inch laptop or 65-inch TV), pipe and tubing diameters (1-inch plumbing, 2-inch exhaust), and shoe sizes in Anglo-Saxon countries. Construction lumber, photographic prints, paper sizes (US Letter is 8.5 × 11 in), and rainfall in the US all use inches. The inch relates to the millimeter (25.4 mm = 1 in exactly), the foot (12 in = 1 ft), and the yard (36 in = 1 yd). Subdivisions in fractions (½, ¼, ⅛) remain common in carpentry.
- Screen and monitor diagonals worldwide (phone, tablet, TV)
- US and UK shoe sizes
- Industrial pipe and fitting diameters
A 65-inch TV has a 165 cm diagonal. A smartphone screen is typically 6–7 inches. Standard copper plumbing in the UK is ½ inch or ¾ inch.
What is the Millimeter?
The millimeter equals one thousandth of a meter (0.001 m) and is the precision unit of choice in engineering, manufacturing, electronics, and meteorology. Its small size makes it ideal for tolerances in mechanical parts, paper thickness, and rainfall measurements. A standard credit card is 0.76 mm thick, and a sheet of office paper is about 0.1 mm. The millimeter is the universal unit for tire-tread depth, weather-station rainfall reports, and 3D printer resolution. It relates to the centimeter (10 mm = 1 cm), the inch (25.4 mm = 1 in exactly), and the micrometer (1 mm = 1,000 µm). Engineering drawings worldwide default to millimeters for dimensions, except in the United States where inches remain dominant in mechanical engineering.
- Rainfall measurements in weather reports
- Precision engineering and manufacturing tolerances
- Medical imaging — tumor and wound size
A 2 euro coin is 25.75 mm across and 2.2 mm thick. Rainfall of 50 mm in 24 h is a red-warning event in most of Europe.