Numerous evolutionary models explore the trade-off between offspring size and offspring number. However, such models often fail when the number of offspring is small because optimal litter size (or litter size at optimal offspring size) may fall between the necessarily integer values for real litters. This paper extends a classic model for optimal investment per offspring to the case of small litters and predicts that range in offspring size and the largest (smallest) offspring size should decline (increase) with increased litter size. Application of the model to egg size data from a poeciliid fish,Gambusia hubbsi, reveals a surprisingly close approximation to the largest offspring size and variation in offspring size at small litter sizes.