A golf green measuring device according to the present invention includes a plurality of spaced apart rails attached to an enclosed structure. The structure includes a control unit including a microcontroller, circuitry, a battery, a display and a level indicator. The rails include infrared emitters and detectors that sense a golf ball traveling through the enclosed structure. The microcontroller measures the elapsed time the golf ball travels between a pair of detectors disposed at the rail front end and the elapsed time the golf ball travels between another pair of detectors disposed at the rail rear end. The change in velocity or deceleration of the golf ball is determined based on the measured time intervals and converted into a speed value. The computed speed value is displayed on a device display. The device may include an optional printer to provide a hardcopy of the measurement.