What is inch?
An inch is a unit of length in imperial and US customary systems equal to 1/12 of a foot. It is widely used for screen sizes, display resolutions, pipe diameters, and small-scale measurements in everyday contexts.
Real-world uses
Inches are used throughout the United States, Canada (partially), and the UK for screen sizes, pipe diameters, lumber dimensions, and screw/bolt specifications. Display sizes for monitors, TVs, and phones are universally quoted in diagonal inches.
History
The inch has ancient origins, traditionally defined as the width of a man's thumb or three barleycorns laid end to end. It was standardized internationally in 1959 as exactly 25.4 mm, reconciling slight differences between British and American definitions.
Common mistakes
Assuming inch fractions are decimal—1/8 inch is 0.125 inches, not 0.18. Also, confusing nominal lumber sizes (a "2x4" is actually 1.5 × 3.5 inches) with actual inch measurements.
What is centimetre?
A centimetre is a metric unit of length equal to one hundredth of a metre. It is commonly used for everyday measurements such as clothing sizes, body height, and small object dimensions.
Real-world uses
Centimetres are widely used in clothing measurements, body height in medical records (outside the US), screen sizes in some markets, and school rulers. Tailors and dressmakers rely on centimetre tape measures for precise garment fitting.
History
The centimetre was established as part of the original metric system in the 1790s. It served as the base length unit in the now-superseded CGS (centimetre-gram-second) system used extensively in physics until the mid-20th century.
Common mistakes
Forgetting that there are 2.54 cm in one inch, not 2.5. Also, confusing cm² (area) with cm (length) when specifying material dimensions.
When is this conversion used?
Converting between inch and centimetre is common when working across metric and imperial systems, such as international trade, travel between countries with different measurement standards, or following instructions from a different region. Screen sizes, paper dimensions, and clothing measurements often require converting between centimetres and inches, especially when shopping internationally.
Worked examples
1 inch = 2.54 centimetre
1 centimetre = 0.01 metre
How to convert inch to centimetre
To convert inch to centimetre, multiply the value by 2.54.
To convert centimetre back to inch, multiply by 0.39370079.
Measurement standards
The metre is one of seven SI base units, maintained by the International Bureau of Weights and Measures (BIPM). Since 2019, it is defined by fixing the numerical value of the speed of light in vacuum to exactly 299,792,458 metres per second.
Did you know?
A human hair is roughly 70 micrometres wide, while a single gold atom measures about 0.144 nanometres in diameter — meaning you could line up nearly half a million atoms across the width of one hair.
Quick reference: inch to centimetre
| inch | centimetre |
|---|---|
| 0.1 | 0.254 |
| 0.5 | 1.27 |
| 1 | 2.54 |
| 2 | 5.08 |
| 5 | 12.7 |
| 10 | 25.4 |
| 25 | 63.5 |
| 50 | 127 |
| 100 | 254 |
| 250 | 635 |
| 500 | 1,270 |
| 1,000 | 2,540 |
Common values
| inch | centimetre | |
|---|---|---|
| Height of a door | 82.67716535 inch | 210 centimetre |
| Basketball court length | 1,102.36220472 inch | 2,800 centimetre |
| Football field (soccer) | 4,133.85826772 inch | 10,500 centimetre |
| Marathon distance | 1,661,220.47244094 inch | 4,219,500 centimetre |
| Altitude of a cruising airplane | 420,000 inch | 1,066,800 centimetre |