Procedures and mathematical relationships were developed to describe seed size distributions for Florigiant, Florunner, and Starr peanut (Arachis hypogaea L.) varieties. Of six standard probability distributions studied, the normal and logistic distributions provided the best fit for the experimental data, These two distributions were therefore fitted to seed size data for several lots of peanuts. For each lot both the normal and logistic distributions provided an excellent fit to the experimental data, but the logistic was slightly superior. Differences between experimental and calculated values were greatest for lots that were the least or most mature. A logistic distribution was also fitted to the average of all data for each variety. These relationships may be used to better relate seed size to quality, marketing, shelling, and processing. They will also be useful in research studies of the effects on seed size of such variables as variety, agronomic practices, climate, soil moisture, and harvest dates.