Contraction of an excisional wound can be described by a decaying exponential with a non-zero asymptote between days 6 and 39 after wounding. Regardless of size or shape, the contraction-rate constant is invariant within age- and species-matched animals. Differently shaped wounds of the same size contract at the same rate during the exponential period. Shape exerts its effect prior to the onset of contraction by defining the size of the wound entering the exponential period. Perimeter is the factor by which shape determines size.