A measuring apparatus is provided for measuring a diameter of a hole. The measuring apparatus includes a sensor unit, a data processing unit, and a display unit. The sensor unit includes a probing member. The probing member includes a plurality of probes with contact ends being arranged on a circumference, and a plurality of angle sensors. The probes are capable of contacting the inner surface of the hole. The angle sensors are arranged on each of the probes to obtain digitally an angle value of each splaying probe contacting the inner surface of the hole. The data processing unit is configured for receiving the angle value generated by the sensor unit and computing the diameter of the hole according to the value of an angle. The display unit is configured for displaying the diameter computed by the data processing unit. A method is also provided for using the measuring apparatus.