Hi Grant, yes a head length is from the tip of the head to the end of the gill plate. Now, if you take this length and apply it to the length of the koi, it should be at least 5 and 1/2 headlength long (this includes the head length). Anything shorter will give you a stumpy football-shaped koi. Longer is better as long as there is a decent hump and a broad shoulder. Hope the pros will chime in.
