I'm 5'7/8 and 11 stone.
I'm not fat.
The thing is, weight apportions itself to different parts of the body for each individual, so 2 people could be same height, weigh the same, and have completely diff physiques;.
A 'healthy' weight can be calculated by BMI tests, but, this pretty much excludes athletes, as muscle is denser then fat, therefore you could be classed as overweight due to being hench.