Put your feet together and stand straight. Take the distance between your knees and divide by 2. Call this X.
Measure the distance between your knee and your heel. Call this Y.
Measure the distance between your crotch and your knee. Call this Z.
(Make sure all units are the same)
Tibia angle = arcsin (X/Y) (call this angle A)
Femur angle = arcsin (X/Z) (call this angle B)
Added height = Y(1-cosA) + Z(1-cosB)
There you go. High school trigonometry is useful after all!
In reality, it doesn't work like this. Device error, bone growth rate, muscles, ... a lot of things will factor in.
Do not say it so sure like this when you do not know what it is really like.