Prefixes can be used with defined unit names to expand the scope of unit names. You can, for example, create kilometers from meters by adding the prefix "kilo".
ans = 1000 m
The answer is returned as 1000 meters. The term "kilometer" is a standard and well recognized term. Prefixes can also be used used in conjunction with terms that are not as well recognized. For example, the diameter of the earth at the equator is
If the earth were perfectly spherical, the volume of the earth would be
Just for fun, the volume of the earth can be expressed in "megateaspoons".
ans = 1.96396e+020 megateaspoons
yatto 1e24 zetta 1e21 exa 1e18 peta 1e15 tera 1e12 giga 1e9 mega 1e6 kilo 1e3 hecto 1e2 deka 10 deci 0.1 centi 1e-2 milli 1e-3 micro 1e-6 nano 1e-9 pico 1e-12 femto 1e-15 atto 1e-18 zepto 1e-21 yacto 1e-24