A new procedure using a student-friendly least-squares multiple linear-regression technique utilizing a function within Microsoft Excel is described that enables students to calculate molecular constants from the vibronic spectrum of iodine. This method is advantageous pedagogically as it calculates molecular constants for ground and excited I[subscript 2] states simultaneously, directly from equations of energy for vibronic transitions. In addition, this method calculates the standard errors of the molecular constants and allows students to comment on the accuracy of the data. (Contains 4 tables and 2 figures.)