It's fairly simple indeed.

Installation:
On Ubuntu:
apt-get install units
On Mac OSX:
brew install gnu-units
Example:
1024 bytes to MB

Ubuntu

units -v 1024byte megabyte

Mac OSX

gunits -v 1024byte megabyte

And the result:

1024byte = 0.001024 megabyte
1024byte = (1 / 976.5625) megabyte