Spent a few years working with leather, about half my life so I'll tell you of my experience. If you are covering a chair with a padded seat, use upholstery leather, you can buy it easily in full skins. 4 oz. is heavy enough and it will have some stretch to it. It its a padded seat or cushion then heavier leather will have a tendency to stretch less and may pull loose from the tacks or staples . Ive used some 4 oz oiled leather that makes great seat material.