In the present study, the inertia moment and friction coefficient of direct current (DC) and permanent magnet synchronous (PMS) motors were calculated. Retardation experiment was carried out to calculate these values, and current, voltage and rotation values of the motor were calculated with the help of sensors. The measurement results were read with the help of a card designed using dsPIC30F4013, a high-performance digital signal controller. Power and torque values were calculated using the data transferred into the computer. Graphs showing power-velocity and velocity-time were drawn through the use of the values that were measured and calculated. Power-time graph was obtained by using these two graphs. To be able to carry out numerical procedures using the power-time graph created, curve fitting method in MATLAB was used, and mathematical expression of the graph was obtained. The kinetic energy stored in the motor was calculated using the mathematical expression mentioned, and the inertia moment was found using this value. The friction coefficient was calculated using the torque equation for stationary running of the motor at rated speed. The results of the simulation carried out in MATLAB by using the calculated coefficients and those of the experiment were compared. © (2014) Trans Tech Publications, Switzerland.