<P> 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 . </P> <P> The terms micron and (occasionally) millimicron are often used instead of micrometre (μm) and nanometre (nm), but this practice is officially discouraged . </P> <Table> SI multiples for metre (m) <Tr> <Th_colspan="3"> Submultiples </Th> <Td> </Td> <Th_colspan="3"> Multiples </Th> </Tr> <Tr> <Th> Value </Th> <Th> SI symbol </Th> <Th> Name </Th> <Th> Value </Th> <Th> SI symbol </Th> <Th> Name </Th> </Tr> <Tr> <Td> 10 m </Td> <Td> dm </Td> <Td> decimetre </Td> <Td> 10 m </Td> <Td> dam </Td> <Td> decametre </Td> </Tr> <Tr> <Td> 10 m </Td> <Td> cm </Td> <Td> centimetre </Td> <Td> 10 m </Td> <Td> hm </Td> <Td> hectometre </Td> </Tr> <Tr> <Td> 10 m </Td> <Td> mm </Td> <Td> millimetre </Td> <Td> 10 m </Td> <Td> km </Td> <Td> kilometre </Td> </Tr> <Tr> <Td> 10 m </Td> <Td> μm </Td> <Td> micrometre </Td> <Td> 10 m </Td> <Td> Mm </Td> <Td> megametre </Td> </Tr> <Tr> <Td> 10 m </Td> <Td> nm </Td> <Td> nanometre </Td> <Td> 10 m </Td> <Td> Gm </Td> <Td> gigametre </Td> </Tr> <Tr> <Td> 10 m </Td> <Td> pm </Td> <Td> picometre </Td> <Td> 10 m </Td> <Td> Tm </Td> <Td> terametre </Td> </Tr> <Tr> <Td> 10 m </Td> <Td> fm </Td> <Td> femtometre </Td> <Td> 10 m </Td> <Td> Pm </Td> <Td> petametre </Td> </Tr> <Tr> <Td> 10 m </Td> <Td> am </Td> <Td> attometre </Td> <Td> 10 m </Td> <Td> Em </Td> <Td> exametre </Td> </Tr> <Tr> <Td> 10 m </Td> <Td> zm </Td> <Td> zeptometre </Td> <Td> 10 m </Td> <Td> Zm </Td> <Td> zettametre </Td> </Tr> <Tr> <Td> 10 m </Td> <Td> ym </Td> <Td> yoctometre </Td> <Td> 10 m </Td> <Td> Ym </Td> <Td> yottametre </Td> </Tr> <Tr> <Td_colspan="7"> Common prefixed units are in bold face . </Td> </Tr> </Table> <Tr> <Th_colspan="3"> Submultiples </Th> <Td> </Td> <Th_colspan="3"> Multiples </Th> </Tr>

Rank these si distance units from smallest to largest μm am fm nm mm cm m km gm tm mm em pm
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