An ultrasonic instrument includes a body and a shaft assembly extending distally from the body. The shaft assembly includes an acoustic waveguide. The instrument further includes an end effector including an ultrasonic blade. The ultrasonic blade is in acoustic communication with the acoustic waveguide. The instrument further includes a sensor configured to sense at least one characteristic of the shaft assembly and/or the end effector. The end effector is configured to be activated at varying power levels based on the at least one characteristic sensed by the sensor.