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4. Large and small units

The SI scale of units is metric, and is based on factors of ten. Specific prefixes are given to units that are factors of one thousand larger or smaller than the base unit. The following table uses the metre as an example:

Names and magnitudes of commonly used SI unit prefixes. Unit names are hyphenated to make them easier to read

Unit name Symbol Value
peta-metre Pm 1 000 000 000 000 000 m
tera-metre Tm 1 000 000 000 000 m
giga-metre Gm 1 000 000 000 m
mega-metre Mm 1 000 000 m
kilo-metre km 1 000 m
metre m 1 m
milli-metre mm 0.001 m
micro-metre μm 0.000 001 m
nano-metre nm 0.000 000 001 m
pico-metre pm 0.000 000 000 001 m
femto-metre fm 0.000 000 000 000 001 m
atto-metre am 0.000 000 000 000 000 001 m