Questions concerning the minimum space requirement for intensively kept pigs in relation to their welfare have been an issue of interest for many decades. Recently, the discussion about these questions has intensified, as there is a growing concern among western societies about the welfare of intensively kept pigs. Most studies on space allowances or requirements have been assessed in experiments where the performance of the pig is predominant measure. This suggests that there is no need to house pigs at an area larger than the area below which production decreases. However, from a welfare perspective this is questionable. This study focused on the lying postures, space occupation and percentage of space-sharing in pigs, in order to develop a theoretical framework on spatial requirements for pigs, e.g. for pen design legislative purposes. Pigs were housed at thermoneutral conditions, on 60% solid and 40% slatted floors, in groups of eight from 25 to 100 kg live weight. Behaviours of the pigs were recorded at approximately 30, 50, 80 and 100 kg live weight, in order to gain an insight into their space use and space requirements. The results showed that pigs of all weight categories lie down for a greater part of the day. Based on the behavioural observations carried out, present study confirmed that the floor area occupied by lying pigs at thermoneutral conditions should on average be based on the estimated floor area for half recumbent pigs (the animal is lying half on the side and half on the belly), i.e. area = 0.033 x body weight0.66 which in turn exceeds the recommended minimum space requirements for commercial practices in EU. The present study however, does of course not answer the questions whether pigs actually need an amount space that goes beyond recommendations generally based on production performance studies. Additional validation experiments, studying the welfare relevancy of those behavioural expressions should be carried out in order to answer this question.