GNU Units

https://www.gnu.org/software/units/

http://ftp.gnu.org/gnu/units/windows/

Java

http://sourceforge.net/projects/jconvert/

Python

https://pint.readthedocs.org/en/0.6/tutorial.html

Wikipedia

https://en.wikipedia.org/wiki/Metric_prefix

Other links

http://ptec107.wikispaces.com/file/view/conversion_factors.pdf