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 sport

Combat sport

A Combat sport, also known as a Fighting sport, is a competitive contact sport where two combatants fight against each other using certain rules of engagement , typically with the aim of simulating parts of real hand to hand combat...

s such as boxing

Boxing

Boxing, also called pugilism, is a combat sport in which two people fight each other using their fists. Boxing is supervised by a referee over a series of between one to three minute intervals called rounds...

 or mixed martial arts

Mixed martial arts

Mixed Martial Arts is a full contact combat sport that allows the use of both striking and grappling techniques, both standing and on the ground, including boxing, wrestling, Brazilian jiu-jitsu, muay Thai, kickboxing, karate, judo and other styles. The roots of modern mixed martial arts can be...

 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

The Ring (magazine)

The Ring is an American boxing magazine that was first published in 1922 as a boxing and wrestling magazine. As the sporting legitimacy of professional wrestling came more into question, The Ring shifted to becoming exclusively a boxing oriented publication...

magazine maintains a pound for pound rank

Ring Magazine pound for pound

The Ring Magazine Pound for Pound is the official list of the current pound for pound professional boxing rankings distributed by The Ring.-Top 10 rankings:-See also:* List of current world boxing champions* List of boxing weight classes...

 of fighters. ESPN.com

ESPN

Entertainment and Sports Programming Network, commonly known as ESPN, is an American global cable television network focusing on sports-related programming including live and pre-taped event telecasts, sports talk shows, and other original programming....

has a list for mixed martial artists.