A model for the rate of growth of short cracks is proposed. This is adapted from a model commonly used for describing the behaviour of long cracks. The physical properties of the microstructure of the material which influence short crack behaviour are taken into account. The model differs from other methods which have been used to model short cracks, in that it focuses on the behaviour of a population of individual cracks; that is the growth of each crack is considered. Alternative methods have used overall damage criteria, such as microcrack density, to describe the behaviour of the population of short cracks.