;) I'm an engineer. I don't even calculate a tip without my calculator. :)
( when i was in college. we had an instructor that always would say 'check my math, I'm an engineer' if he did a calc in his head vs on a calculator. )
but yeah.. whichever way you want to run the calc from may be easier if you think in liters or cubic inches.
hte whole deal is fuzzy anyway as decimals are dropped and things are rounded... reminds me of my statistics class. Only math class I ever took that using the word 'about' in an answer could be / was correct nomenclature... :) hated that class.. :)