I'm not sure if this really helps:
Energy = Mass*(speed of light)^2
You probably already know this. However, in case you don't, I hope this helps. As you can see, this number can get very large. Anyway, imagine a hydrogen atom - essentially a proton. This hydrogen atom has a very small mass (can't remember what it was in kg). To find the energy of this hydrogen atom- just multiply by the square of the speed of light - which should amount to a fairly large number in comparison to the mass of a hydrogen atom. This is because the theorem above states the amount of energy that the mass would be turned into if it was turned into raw energy!
Once again- hope this helps!