Millimetre
The millimetre or millimeter is a unit of length in the International System of Units, equal to one thousandth of a metre, the SI base unit of length.
- 1 metre = 1000 millimetres
- 1 centimetre = 10 millimetres
- micrometres
- nanometres
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
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
To support layout compatibility with East Asian scripts, Unicode includes square symbols for:- Millimetre –
- Square millimetre –
- Cubic millimetre –
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.
- 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.
- The smallest visible object to the human eye is around 0.02–0.04 mm.
- A typical sheet of paper is between 0.07 mm and 0.18 mm thick; copy paper is about 0.1 mm.