0.7 Less common metric prefixes by Benjamin Crowell, Light and Matter  licensed under the Creative Commons Attribution-ShareAlike license.

0.7 Less common metric prefixes

The following are three metric prefixes which, while less common than the ones discussed previously, are well worth memorizing.

prefix	meaning	example
mega-  M	106	6.4 Mm  = radius of the earth
micro- μ	10-6	10μm = size of a white blood cell
nano-  n	10-9	0.154 nm  = distance between carbon nuclei in an ethane molecule

Note that the abbreviation for micro is the Greek letter mu, μ - a common mistake is to confuse it with m (milli) or M (mega).

There are other prefixes even less common, used for extremely large and small quantities. For instance, 1 femtometer= 10^-15 m is a convenient unit of distance in nuclear physics, and 1 gigabyte=`10^9` bytes is used for computers' hard disks. The international committee that makes decisions about the SI has recently even added some new prefixes that sound like jokes, e.g., 1 yoctogram= 10^-24 g is about half the mass of a proton. In the immediate future, however, you're unlikely to see prefixes like “yocto-” and “zepto-” used except perhaps in trivia contests at science-fiction conventions or other geekfests.

self-check: Suppose you could slow down time so that according to your perception, a beam of light would move across a room at the speed of a slow walk. If you perceived a nanosecond as if it was a second, how would you perceive a microsecond?
(answer in the back of the PDF version of the book) 

0.7 Less common metric prefixes by Benjamin Crowell, Light and Matter  licensed under the Creative Commons Attribution-ShareAlike license.