The main purpose of this paper is the evaluation of the shunt active power filter apparent power ratio between the apparent power generated by the source power system to the load and the compensation apparent power produced by the shunt APF to force the currents circulating toward the source to be sinusoidal and balanced. This ratio allows defining the compensations capability for different perturbations in AC power system such as current unbalance, phase shift current and undesired harmonics generated by non linear load. This capability is determined by the maximum rate of the apparent power that can be delivered. In this paper a method of evaluation of this ratio is proposed, it is based on the definition of the effective apparent power as defined in IEEE 1459-2000 which was proved to be a suitable amount to be concerned in the design process of different devices.