The Standard Length is little longer than a stock strap, perfect for using as a traditional neck strap or hanging off one shoulder. Also works as a cross body strap for most people up to about 170cm (5'7" tall).
Our Long Length straps are 25cm longer than our Standard Length which makes them better for wearing across the body for people over 170cm (5'7") tall.
More detailed info on choosing a strap here.