To size up a person, decide that they can fit into a bag/sack (preferably of the burlap or potato variety) that you may or may not be able to carry.
Then proceed to abduct said individual for whatever purposes you would abduct a person, employing a bag/sack (preferably of the burlap or potato variety) if it so pleases you.
"I am going to abductorsize that person!" - 1
"Are you sure that person is not too big for you?" - 2
"Screw it, I am doing it, call the ambulance" - 1