An accurate knowledge of the power dissipation and efficiency of an inverter-fed motor is essential, whereas a precise measurement with a high resolution of measurement points is very time consuming and cost intensive. In the standard IEC 60034-2-3, seven standardized measuring points are used to determine the losses and efficiencies throughout the whole base speed range of an electrical machine. However, the used correlation is not applicable to the fieldweakening and overload range, whereas those regions are of enormous importance for a speed-variant drive system. In this contribution, we present an approach to extend the existing interpolation approach in IEC 60034-2-3 to estimate the losses and efficiencies between standstill and twice the rated speed as well as between no-load operation and twice the rated torque. The approach is based on the seven standardizes measurement points and no additional measurement is needed. Furthermore, the influence of a switching from a star-connection to a delta-connection and from a star-connection to a double star-connection is investigated.