My 16.1 TBx who normally wears 6ft 6 rugs and some 6ft 3, has a 6ft 3 Thermatex which is a little on the big side so I would say possibly a 6ft. I also tried his rug on a friends horse who is normally a 6ft 9 rug and it fitted perfectly.
i spoke to a lady on the thermatex stand at YHL and she said its a size smaller than normal, my boy is 6ft 9in in turnout and 6ft 6in in the stable, so i got a 6ft 3in and it fits lovely!
Im still so confused, he is wearing a w.beeta t/o in 6ft6, Amigos in 6ft3 which are SNUG, Axiom 6ft3 which is fine, Stables are all 6ft.6 as are fleeces - Im guessing a 6ft 3 will be the best bet really then
My horse varies between 6' and 6'3" rugs - I've got a 6' Thermatex and it's slightly on the small side - but he is very chunky.
If he's a chunky build I'd go for the same size, if he's slim I'd go a size down.
Personally, if I'm buying a rug for traveling/shows I would go for two sizes smaller than I would a turnout rug. Travel/show rugs don't need to cover the bum and if they do, I find the rug gets drawn back when traveling. Add that to the fact that Thermatexes are quite stretchy, the I would def go for two sizes smaller.