# Mass-energy equivalence where's the arbitrary constant?

1. Oct 31, 2008

### hatsoff

I'm curious about the famous formula, $$e=mc^2$$ . Since mass can be measured in any of several unit systems, shouldn't the formula read $$e\propto mc^2$$ ?

Thanks!

Last edited: Oct 31, 2008
2. Oct 31, 2008

### Staff: Mentor

No, you just need to keep the units consistent throughout the equation.