Prior to state sanctioning, weight classes were not mandatory since the competitions were held without the approval of the athletic commissions. For instance, the Ultimate Fighting Championship introduced two weight classes at UFC 12: heavyweight, which grouped competitors above 200 lb, and lightweight, which grouped competitors under 200 lb. Weight divisions underwent many changes in the ensuing years, but the ability of promotions to autonomously decide their own weight classes eventually disappeared after athletic commissions began supervising mixed martial arts. In 2000, the Unified Rules of Mixed Martial Arts were codified by the New Jersey State Athletic Commission. The California State Athletic Commission had worked extensively on regulation, but their sanctioning of MMA was not implemented due to state governmental issues surrounding the process. California officially sanctioned MMA on December 28, 2005, using the ruleset it helped devise five years previously. Since then, to create uniformity, all state commissions in the United States that regulate mixed martial arts have assimilated these rules into their existing unarmed combat competition rules and statutes. For a promotion to hold mixed martial arts events in a state-sanctioned venue, the promotion must abide by the state athletic commission's body of rules for weight limits. The Unified Rules designate limits for fourteen different weight classes in mixed martial arts; all definitions and measurements are in pounds. The strawweight class was added in 2015. The super lightweight, super welterweight, super middleweight, and cruiserweight classes were added in July 2017.
With no state or government laws regarding weight class restrictions, organizations in other countries are free to schedule bouts with little regard for weight differential. However, due to the increasingly competitive and international nature of the sport, weight limits have been set by the promotions themselves usually in alignment with the Unified Rules, as maintaining standard weight classes is seen as fair and standard for all competitors. One notable exception to this standard is Asian promotion ONE Championship, which adopted higher weight limits as well as pre-fight urinalysis in order to discourage weight cutting. This was brought about by the 2015 death of Chinese fighter Yang Jian Bing, who died during training camp for a fight after heavily dehydrating himself to make weight. In ONE, for instance, the light heavyweight limit is 102 kilograms, nine kilos/20 pounds more than the Unified Rules' light heavyweight standard.
Women
Weight limits in women's MMA mostly follow the Unified Rules' limits, but organizations that recognize women's championships usually only have titles at the lower end of the table. UFC, for example, recognizes women's titles in the strawweight, flyweight, bantamweight and featherweight classes. Some organizations that recognize women's championships also sanction a separate atomweight title with a limit.
