SI Prefixed Forms of Metre
SI prefixes are often employed to denote decimal multiples and submultiples of the metre, as shown in the table below. As indicated in the table, some are commonly used, while others are not. Long distances are usually expressed in km, astronomical units (149.6 Gm), light-years (10 Pm), or parsecs (31 Pm), rather than in Mm, Gm, Tm, Pm, Em, Zm or Ym; "30 cm", "30 m", and "300 m" are more common than "3 dm", "3 dam", and "3 hm", respectively.
The term micron is often used instead of micrometre, but this practice is officially discouraged.
| Submultiples | Multiples | |||||
|---|---|---|---|---|---|---|
| Value | Symbol | Name | Value | Symbol | Name | |
| 10−1 m | dm | decimetre | 101 m | dam | decametre | |
| 10−2 m | cm | centimetre | 102 m | hm | hectometre | |
| 10−3 m | mm | millimetre | 103 m | km | kilometre | |
| 10−6 m | µm | micrometre | 106 m | Mm | megametre | |
| 10−9 m | nm | nanometre | 109 m | Gm | gigametre | |
| 10−12 m | pm | picometre | 1012 m | Tm | terametre | |
| 10−15 m | fm | femtometre | 1015 m | Pm | petametre | |
| 10−18 m | am | attometre | 1018 m | Em | exametre | |
| 10−21 m | zm | zeptometre | 1021 m | Zm | zettametre | |
| 10−24 m | ym | yoctometre | 1024 m | Ym | yottametre | |
| Common prefixed units are in bold face. | ||||||
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