In my opinion, Followship is the single measure that can tell you how great of a leader you are.
A leader has the ability to motivate, collaborate with, and influence others to commit to and do what is on his/her agenda. For this to happen, you need people who will commit to following this leader.
A leader would have followers who are not just his/her direct reports; followers would be from other teams who will do whatever they can to assist this leader be successful.
How do you measure followship? Is someone doing something for you because they fear they must? Or because they want to?
True followers will be engaging and will continue to challenge the leader by providing constructive feedback. Followers who follow because they have to will not be engaging and will simply do what you ask them unwillingly with negative comments and attitude.
A leader must have followers; without followers you have no one to lead.