Various attempts have been made to fully explain the mechanism by which a body has inertial mass. Recently it has been proposed that this mechanism is as follows: when an object accelerates in one direction a dynamical Rindler event horizon forms in the opposite direction, suppressing Unruh radiation on that side by a Rindler-scale Casimir effect whereas the radiation in the other side is only slightly reduce by a Hubble-scale Casimir effect. This produces a net Unruh radiation pressure force that always opposes the acceleration, just like inertia, although the masses predicted are twice those expected, see \cite{Mc6}. In a later work an error was corrected so that its prediction improves to within 26\% of the Planck mass, see \cite{GM}. In this paper the expression of the inertial mass of a elementary particle is derived from the holographic scenario giving the exact value of the mass of a Planck particle when it is applied to a Planck particle.The author thanks the referee for the comments and suggestions that helped to improve this paper. The author is partially supported by a MINECO/ FEDER grant number MTM2014-53703-P and an AGAUR (Generalitat de Catalunya) grant number 2014SGR 1204