Some show what is often called 'Prim Height' which comes very close to the true mesh height of an avatar. Some show (stupidly) the same Agent Height as Linden lab viewers do. But as said, they come pretty close anyway. They will display pretty closely the true mesh height of an avatar - they are a bit off too however. Some third party viewers show more correctly the actual avatar mesh height - instead of the 'Agent Height'. It would mean to find a way to measure/calculate the vertical distance between avatar's lowest and highest vertices, and code that into the viewer. I guess it might be complicated task to code the exact avatar's mesh height into the viewer.
Linden Lab is well aware of this, but it seems the task is too difficult for them to correct. Causes a lot of confusion about avatar height. The sad thing is that lots of people assume that the height shown in Linden Lab viewers is avatar's mesh height. The avatar mesh itself is taller than this Agent Height reported by Linden Lab viewers. Linden lab viewers show what is called 'Agent Height'.
Is Appearance information standard between all viewers? If so, why not just go into appearance and see the height right there? You can change it to metric there as well.
