It can be shown that

1 a.m.u $=1.66 \times 10^{27}\,kg$.

According to Einstein, mass energy equivalence

$E = mc ^2$

Where $m =1.66 \times 10^{-27}\, kg$

$C =3 \times 10^8\, m / sec$, we get

$E =1.49 \times 10^{-10}\, J \left(1 Mev =1.6 \times 10^{-13}\, J \right)$

$E =\frac{1.49 \times 10^{-10}\, J }{1.6 \times 10^{-13}}\,Mev$

$E =931.25\,Mev$

Hence a change in mass of $1\,a. m.u$ (called mass defect) releases an energy equal to $931 \,Mev$.

$1\,amu =931\,Mev$ is used as a standard conversion.