6 foot 2
His height per imdb. That has to be wrong. No taller than 5 foot 8.
shareAmell is listed at 6'1", he may actually be slightly shorter. Gustin could be 6'0" or even 6'1". He does have a tall frame. On Arrow, it would have been camera tricks to make Amell appear more imposing. This happens very often when it comes to a Protagonist. In this show, Barry Allen is shown as being very tall aswell. In the show, he appears to be as tall as Jesse L. Martin
It's not just camera tricks that make Stephen look taller since in all of their photos together (on and off the set) Stephen looks about an inch taller than him. So if his listed height is correct, than Grant is no more (or less) than 6'.