It is recommended that gestating sows of various weights should be kept in different sizes of stalls. However, the proper size of stall has not been well defined. A study was conducted to evaluate stall width by assessing the interaction between stall width and sow size on behaviour. As stall width decreased, sows spent less time standing, more time sitting, and their udders extended into the adjacent stall more frequently. Using udder extension during less than 50% of lateral lying as a criteria for stall width, a 65 cm (26”) stall is adequate for gilts and small sows, but a 70 cm (28”) stall is required for larger sows if in stalls for the entire gestation period.