Basically you have to consider the effect of harmonic waves, but there are two ways as below.
1. Refer to the recommended rated current by inverter manufacturer.
2. Calculate a load current from power supply capacity described in inverter catalog or other materials, and consider 1.4 times of the value or more as the rated current. It may need 2 times or more ,depending on current waves (Distortion factor, Peak factor, Harmonic component).