The Linux command ‘units’ may or may not be installed on your system. If not, if you use synaptic or apt, type (at the prompt)
sudo apt-get install units
or equiviliant for other distributions. Then type in the word “units” and play around. Here are a few sample outputs:
The program is a little clunky. You have to know the specific codes for each type of measurement, though ‘units’ will figure out what you mean sometimes. To exit, type ctrl-D. There is a way to use this utility in a script. That and other details are found in the manual.