Engineers think that pole embrace size of a PM BLDC motor affects directly the efficiency and the torque. Dealing with the experimental research, in the study we have investigated the effects of narrowing rotor pole embrace step by step by changing sizes parametrically. By doing so, high efficiency and low cogging torque would have been obtained for a 20 W PM BLDC motor. In order to do this, pole arc to pole pitch ratio of magnets at the rotor poles has been changed parametrically (0.5 to 1) by genetic algorithm methodfirst. Then the electromagnetic field dispersions, output parameters of the motor, new rotor constructions have been obtained; and new pole embrace has been derived from the variation of pole arc to pole pitch ratio. We have also calculated the magnetic flux distribution, output power, torque, cogging torque and efficiency values analytically and the effects of new pole embrace to motor efficiency and torque have been simulated. The developed 18 slots, 6 poles, surface mounted inner runner configuration rotor machine is proposed as to be used in small dentistry apparatus.