The position of a droppable object (e.g., a cementing plug or drillpipe dart) in a cased wellbore may be determined in real time during a cementing operation. A pressure data acquisition system is installed at a wellsite and a pressure transducer is installed at the wellhead. As the droppable object travels through casing it encounters regions with a positive or a negative change of inner cross-sectional dimension. The droppable object generates a pressure pulse as it passes through the regions. The pressure pulse and associated reflections are detected by the pressure transducer, and the signals are processed mathematically to determine the current position of the droppable object.