What is the Relationship between Mass and Inerta?

Inertia is a basic property of the universe: a body tends to continue its motion in a straight line unless acted upon by a force. Force is defined by mass and acceleration, and inertia is not otherwise measurable.

There are two ways to define mass: f=ma and w=mg. The first is mass of inertia and the second is mass of gravitation. Nobody knows any way to prove that these are or are not the same mass.

Sorry for such a lousy answer. but that is all that is currently known.