This paper presents the logic and details of a FORTRAN computer program which fits a two parameter catenary curve, using the method of least squares, to a set of data points arising from an exact size photograph of a dental model. Error is assessed by evaluating the difference between the observed and fitted y values. Finally, the length of the arc is measured. The program is useful in studies related to dental arch form as a part of orthodontic treatment. The measurement of the arc length provides as assessment of space available in the dental arch, which is an important part of treatment planning for the orthodontic patient.