Ellipsometry is commonly employed to evaluate the thicknesses and refractive indices of thin films grown on silicon. To obviate the use of relatively inaccurate graphical techniques in the calculation of film parameters from ellipsometer readings, a computer program, which solves the appropriate equations iteratively, has been written. The program, in Fortran IV, which was developed, primarily, for interactive-mode operation, makes efficient use of computer core and time, and can handle measurements taken from transparent films, comprising up to 50 layers, grown from, or deposited on, silicon substrates.