Toner motion is controlled by electric force, adhesion force, mechanical force, and so on, in the electrophotographic printing process. Adhesion force is an important force. Adhesion force in the absence of electrostatic force is estimated by electric field forced toner jumping. Toner is sprayed on one of a pair of electrodes that are spaced parallel to each other. Voltage increasing at a constant rate is applied to the electrode, and toner jumping starts at the voltage where electric force overcomes adhesion and gravitation forces. From the toner jumping voltage, adhesion force is estimated. Toner diameter, substrate and toner application method dependencies are obtained.