We assume that the mechanical and ventilation power looses p_mec+v and the iron looses P_Fe are known.They can be separated following a no load test. Is also assumed to be known the resistanceR₁, determined with the warmed motor.
For each load, will be measured the input power P₁, the input current I₁, the slip s and is computed

The values are used as follows:
From the power P₁ are subtracted the looses in the stator winding p_J1 = m₁ R₁ I₁² and the iron looses; the electromagnetic power P_M is then obtained and, consequently, the electromagnetic torque T.
The slip s is measured too, so the rotor looses can also be determined p_J2 = s P_M.
If from P_M, the looses p_J2 and p_mec+v are subtracted, the output power P₂ is obtained and consequently, the efficiency h = P₂ / P₁.

The described calculus is performed for different loads and the necessary operation characteristics are experimentally determined.