How is reach determined in fighting?

Question

Is it just the length of the fighters arm? Or is it how far he can punch when taking a step foward? How is it calculated?

Answer 1

Knuckle to knuckle across the back. They do measure arm lengths individually and EVEN measure the wrist, they measure almost everything. Sometimes, a guy may have a wide back, and that adds into the measurement without their arms actually being longer. That is fairly rare though.

Answer 2

Finger tip to finger tip measurement of a fighters wingspan.