We perform lapping experiments on magnetic readers’ and writers’ heads to determine the relationship between the magnetic track width and the electrical lapping guides, used as sensors to control the writer’s and reader’s lapping process. The experimental results are used to construct the model calibration curve and calculate the magnetic track width sensitivity function, defined as the rate of the change of the magnetic track width with respect to the writer’s height. First-principle calculations of this relationship and the magnetic track width sensitivity are also carried out with the Landau-Lifshitz-Gilbert equation using the Object Oriented Micro-Magnetic Framework (OOMMF) software. The modeling from both approaches yields consistent results, and shows that the magnetic track width sensitivity obeys a power-law relation. Consequently, we are able to investigate, predict and compensate the magnetic track width in a lapping process with reasonable accuracy.