Pound for pound is a term to describe how any two things compare when bearing in mind their varying quantities; for example, a tin of tomatoes weighing 250 g and costing $2.50 is more expensive, pound for pound, than one weighing 500 g and costing $4 (as the former costs $1.00 per 100 g and the latter $0.80 per 100 g).
It is used in combat sports such as boxing[1] or mixed martial arts[2] to describe a fighter's value in relation to fighters of different weight classes. As these fighters do not compete directly judging the best fighter pound for pound is subjective and ratings vary. They may be based on a range of criteria including "quality of opposition", factors such as how exciting the fighter is or how famous they are, or be an attempt to determine who would win if all the those ranked were the same size. In boxing, The Ring magazine maintains a pound for pound rank of fighters. ESPN.com has a list for mixed martial artists.[3]