# Natural units question

by JoePhysicsNut
Tags: natural, units
 Mentor P: 11,928 In natural units, c=1. MeV/c^2 is compatible with SI units, MeV is not. $$1kg = 1kg\frac{m^2}{s^2} \frac{s^2}{m^2} = 1J \frac{s^2}{(3\cdot 10^8 m)^2} 9\cdot 10^{16} = 1J/c^2 \cdot 9\cdot 10^{16}$$ $$1J=1C\cdot 1V = 6\cdot 10^{18} q_e \cdot 1V = 6\cdot 10^{12}MeV$$ Therefore: $$1kg = 1J/c^2 \cdot 9\cdot 10^{16} = 5.4\cdot 10^{29}\frac{MeV}{c^2}$$ As you can see, I did not multiply with anything, I just converted units. (a better value for the inverse electric charge would give 5.61 instead of 5.4)