Using the formula E=mc2, the energy released is 3 kg x (3 x 108 m/sec)2 resulting in the value of 27 x 1016 kg-m2/sec2 or 2.7 x 1017 Joules of energy. The value for 1 kilogram of any matter is about 9 x 1016 Joules per kilogram.

E = M c2 M = (E) / (c2) M = (9 x 1016) / (3 x 108)2 = (9 x 1016) / (9 x 1016) = 1 kg Amazing. That's a lotta energy. Like 2.85 gigawatt-years, according to my Casio !