mm = factor of 1/1000
1000 mm = 1 meter
1 mm = 0.001 m

µm = facto of 1/1000000
1000000 µm = 1 meter

km = factor of 1000
1000 m = 1 km

SI (metric) prefixes:

da (deca) = x10 (rarely used)
h (hecto) = x100 (rarely used)
k (kilo) = x1000 = e3
M (Mega) = x1000000 = e6
G (Giga) = x1000000000 = e9
T (Tera) = x1000000000000 = e12
P (Peta) = x1000000000000000 = e15
E (Exa) = x1000000000000000000 = e18
Z (Zetta) = x1000000000000000000000 = e21

d (deci) = /10 = e-1 (rarely used)
c (cent) = /100 = e-2 (rarely used except for cm)
m (milli) = /1000 = e-3
µ (micro) = /1000000 = e-6
n (nano) = /1000000000 = e-9
p (pico) = /1000000000000 = e-12
f (femto) = /1000000000000000 = e-15
a (atto) = /1000000000000000000 = e-18

View the original article here