Stalls remain the primary form of housing in North America. The Canadian code of practise states that stall sizes should increase as the sow increases in body weight. This study looked at the suitability of stall size by examining the relationships among sow size, stall width and sow behaviour. Four widths of gestation stalls were used to house four classes of females based on parity and body weight. It has been suggested that gestating sows be able to lie laterally without having their udder extend into the next stall. At week 3 and week 14 a 24-hour behavioural observation was conducted concerning animal posture and whether the udder extended into the next stall while lying laterally. It was found that in early gestation, week 3, gilts and small sows in 22 inch stalls spent less than 20% of the time with udders extended into the next stall while lying laterally. Medium and large sized sows spent 30% of the time with udders extended into the next stall. At week 14, gilts and small sows housed in 22 inch stalls spent 38%-49% of the time with their udders extended into the neighbouring stall. While following the criterion that udders should not extend into the next stall more than 30% of the time, the results from this study suggest that gilts and small sows be housed in 24 inch stalls and medium and large sows be housed in 26-28 inch stalls. If it is not an option for producers to install different stall sizes, it is suggested that a stall width of 65cm be used to accommodate all sizes of gestating gilts and sows.