To determine the equivalent energy, we use the equation of Einstein's theory of relativity which is expressed as:
Energy = mc^2 where m is the mass and c is the speed of light which is equal to 3x10^8 m/s
Substituting mass and the speed of light,
Energy = .001 kg ( 3 x 10^8 m/s )^2
Energy = 9 x10^13 J