The “mass” of any complex “body” or system of interacting component “bodies”, defined as its resistance to acceleration from rest, includes not just the masses of its components but also terms corresponding to the kinetic energy of their motions relative to one another and to the force fields acting between them.
The numerical factor relating the amount of energy corresponding to a unit of mass depends on the units of time and distance but it is exactly one if we use years for time and light-years for space or approximately one if we use feet for distance and nanoseconds for time. In terms of more normal units like metres and seconds the conversion factor is very large and one unit of mass corresponds to almost 17 powers of ten (ie 100,000,000,000,000,000 ) in units of energy.