Some confusion surrounds the 1,2,3,4 sizing of Devoucoux tack and boots. I hope this can help clear it up. Devoucoux recommends a size guide of : -
Size 1 - to fit ponies up to 14.1hh
Size 2 - to fit horses 14.3hh to 16.1hh
Size 3 - to fit horses 16.3hh to 17.1hh
Size 4 - to fit 17.2hh and above
These are only a guide and obviously not every horse is the same shape, but basically tells you what size to aim for. Size 3 would be classed as extra full and size 4 xx full for the really big type.