# Millimetre online conversion form

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The millimetre (international spelling as used by the International Bureau of Weights and Measures; SI unit symbol mm) or millimeter (American spelling) is a unit of length in the metric system, equal to one thousandth of a metre, which is the SI base unit of length. Therefore, there are one thousand millimetres in a metre. There are ten millimetres in a centimetre.

One millimetre is equal to 1000 micrometres or 1000000 nanometres. Since an inch is officially defined as exactly 25.4 millimetres, a millimetre is therfore equal to exactly ​5127 (≈ 0.03937) of an inch.

### Convert Millimeter to Centimetre

1 mm = 0.1 cm
1 cm = 10 mm

Example: convert 10 mm to cm:
10 mm = 10 × 0.1 cm = 1 cm

Millimetre Ruler with millimetre and centimetre marks
General information
Unit system SI derived unit
Unit of Length
Symbol mm
Named after The metric prefix mille (Latin for “one thousand”) and the metre
Conversions
1 mm in … … is equal to …
micrometres    1×103 μm = 1000 μm
centimetres    1×10−1 cm = 0.1 cm
metres    1×10−3 m = 0.001 m
kilometres    1×10−6 km
inches    0.039370 in
feet    0.0032808 ft

## Contents

1. Definition
2. Informal terminology
3. Unicode symbols
4. Measurement
5. References

## 1.  Definition

Since 1983, the metre has been defined as “the length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second”. A millimetre, 1/1000 of a metre, is therefore the distance travelled by light in 1/299792458000 of a second.

## 2. Informal terminology

A common shortening of millimetre in spoken English is “mil”. This can cause confusion since in the United States, “mil” traditionally means a thousandth of an inch.

## 3. Unicode symbols

For the purposes of compatibility with Chinese, Japanese and Korean (CJK) characters, Unicode has symbols for:

• millimetre (㎜) – code U+339C
• square millimetre (㎟) – code U+339F
• cubic millimetre (㎣) – code U+33A3

In Japanese typography, these square symbols were historically used for laying out unit symbols without distorting the grid layout of text characters.

## 4. Measurement

On a metric ruler, the smallest measurements are normally millimetres. High-quality engineering rules may be graduated in increments of 0.5 mm. Digital callipers are commonly capable of reading increments as small as 0.01 mm.

Microwaves with a frequency of 300 GHz have a wavelength of 1 mm. Using wavelengths between 30 GHz and 300 GHz for data transmission, in contrast to the 300 MHz to 3 GHz normally used in mobile devices, has the potential to allow data transfer rates of 10 gigabits per second.

The smallest distances the human eye can resolve is around 0.02 to 0.04 mm, approximately the width of a human hair. A sheet of paper is typically between 0.07 mm and 0.18 mm thick, with ordinary printer paper or copy paper approximately a tenth of a millimetre thick. 