The UFC currently has a total of nine different weight classes which athletes can compete under, including eight for men and four for women. Other MMA promotions usually have between 14 to 17 recognized weight classes.
The UFC weight classes in the men’s division are as follows:
Flyweight (Minimum: 115lbs Maximum: 125lbs)
Bantamweight (Minimun: 125lbs Maximum: 135lbs)
Featherweight (Minimum: 135lbs Maximum: 145lbs)
Lightweight (Minimum: 145lbs Maximum: 155lbs)
Welterweight (Minimum: 155lbs Maximum: 170lbs)
Middleweight (Minimum: 170lbs Maximum: 185lbs)
Light Heavyweight (Minimum: 185lbs Maximum: 205lbs)
Heavyweight (Minimum: 205lbs Maximum: 265lbs)
The UFC weight classes in the women's division are as follows:
Strawweight (Minimum: None, Maximum: 115lbs)
Women's Flyweight (Minimum: 115lbs Maximum: 125lbs)
Women's Bantamweight (Minimum: 125lbs Maximum: 135lbs)
Women's Featherweight (Minimum: 135lbs Maximum: 145lbs)
Note: In non-title UFC bouts, a relaxation of one pound is allowed between weight classes, but in the case of championship bouts, no such relaxation is allowed.
Why and how were weight classes introduced in the UFC?
Weight classes were introduced in the UFC to ensure that fights take place on a level playing field. Having two fighters competing in the same weight class ensures that the competition is fair, at least in terms of their physical sizes. Therefore, it is the skill of a fighter that determines the outcome of a fight as compared to significant physical advantage due to size.
During the promotion's early days, weight classes weren't mandatory because the fights took place without the approval of the athletic commissions. Back then, the UFC introduced two weight classes. One was heavyweight, which allowed fighters above 200 lbs to compete against each other; and lightweight which allowed fighters below 200 lbs to compete.
In 2000, the New Jersey State Athletic Commission codified the Unified Rules of Mixed Martial Arts and in 2005, the California State Athletic Commission officially sanctioned MMA using the set of rules it introduced five years back. Since then, the State Commissions regulating MMA have incorporated these newly formed rulesets into their existing competition rules and statutes.