Stage transformations in the potassium-graphite intercalation compound have been studied by in situ x-ray diffraction. A precise phase diagram has been determined for the stages up to 7. The stage dependence of $\ensuremath{\Delta}\ensuremath{\mu}(n)$, the stable range of a given stage $n$ in chemical potential, is evaluated from the phase diagram and compared with the theoretical results for the electrostatic model for staging. Time-dependent observation of the stage transformation reveals that only two phases of adjacent stages coexist throughout the process of the stage transformation so that the $c$-axis disorder is insignificant even in the transition region. The kinetics of the stage transformation is also discussed.