it varies really well from my experience I have friends whom play flanker some of them are 6 ft plus and others are shorter then 6 ft like in the 5 ft range, but what a good flanker needs is agility and be able to run fast
It depends. I would say to play flanker in this day and age you'd have to be at least 6 feet tall and 15 stone. that being said, there are some exceptions. For example the ex-england flanker Neil Back who won the World Cup was 5 foot 10 and 14 stone but had an incredible work rate and was 1 of the fittest players in the england set up
Generally, blind side flankers are bigger but ability, pace, agility and heart all count for more than weight and height. McCaw or Waugh werern't what you would really call big but they were very good.
If u mean flanker as in a wing or a slot size depends on the level. but you can compensate for lack of height with speed and agility.
Usually flanker are about 5 feet 9 inches (1.80 cm) but there are flanker that are 6 ft 5 in like Scott Fardy who was capped for Australia 10 times. The weight is often from 95 kg, depending on the height, to 120 or so. For example, Michael Hooper and David Pocock are 1.82 mts and weight 97 kg. I have recently read an article that said that a study in an english university, revealed that the ideal size for a flanker was 1.90 mts and 110 kg as they must have an excellent work rate.
