A - B

From roughly where the wig cap would sit to the rough length you'd like the layers to be. This isn't usually necessary but i want to make sure I don't make the layers too long. 

C - D

From the bottom of the head (where it meets the neck) tp the front of the wig cap (in the middle)
​

E -F 

Apologies this is random google image. 
Back of the ear to the other ear around the head. We might not need this one but lets be thorough so i don't need to keep bugging you for measurements xD; 

Double check circumference (As usual)