The millimetre or millimeter is a unit of length in the International System of Units (SI), equal to one thousandth of a metre, the SI base unit of length.1 metre = 1000 millimetres
1 centimetre = 10 millimetres
Definition
Since 1983, the metre has been defined as "the length of the path travelled by light in vacuum during a time interval of of a second". A millimetre, being of a metre, is the distance light travels in of a second. == Informal terminology ==
Informal terminology
The term "mil" is sometimes used colloquially for millimetre. However, in the United States, "mil" traditionally means a thousandth of an inch, which may cause confusion. == Unicode symbols ==
Unicode symbols
To support layout compatibility with East Asian scripts (CJK), Unicode includes square symbols for: • Millimetre – • Square millimetre – • Cubic millimetre – These symbols are often used in Japanese typography to align unit symbols with text characters. == Measurement ==
Measurement
• On a standard metric ruler, the smallest divisions are typically millimetres. • Precision engineering rulers may show increments of 0.5 mm. • Digital calipers often measure to 0.01 mm accuracy. Examples: • Microwaves with a frequency of 300 GHz have a wavelength of 1 mm. • Using frequencies from 30–300 GHz for millimetre-wave communications allows high-speed data transfer (e.g., 10 Gbps). • The smallest visible object to the human eye is around 0.02–0.04 mm (e.g., a thin human hair). • A typical sheet of paper is between 0.07 mm and 0.18 mm thick; copy paper is about 0.1 mm. == See also ==