Two hundred ninety-six gestating sows were used to determine the physical dimensions of sows in commercial settings. Sows were examined from five farms within a single production model that included identical feed formulation, management practices, herd health, and similar, but not identical, genotypes. Sows were individually weighed, backfat thickness was determined by ultrasound, and body dimensions were determined. Sow body length, height, width (lateral length, left to right from mid-line), and depth (measured as distance from ventral to dorsal extremes) were also determined. Regression procedures were used to model the changes in sow body size in relation to parity, BW, and stage of gestation within and among genotypes. Farm-to-farm variation in sow dimensions for the same genotype was also determined. Least squares means, SD, and 95% upper confidence limits of this sample are presented. Sows increased (P < 0.001) in body dimensions by predicable levels with parity (r2 = 0.92) up to Parity 6, and with advancing pregnancy (r2 = 0.99). Sows of different but related genotypes differed (P < 0.01) in body length, width, height, and depth. Sows of the same genotype, fed the same feed formulation, differed in body dimensions when managed on different farms. Based on mean values and a 95% confidence interval, stall width would need to be at least 72.4 cm to accommodate all sows on the farm. These data and models can be used to design stall sizes and farm floor space needs to meet current animal welfare recommendations. To accommodate the body size of pregnant sows on commercial farms, stall sizes for the majority of sows would need to increase, as would the total floor space needed for a given number of gestating sows individually penned in conventional production systems to meet recently published guidelines.