MMA Weight Classes Explained: UFC, ONE and Amateur

The scale reads 156.0 and the room breathes out. The lightweight limit is 155, but this is not a title fight, so the one-pound allowance means he is a lightweight after all, and the man who spent the last twenty hours in a sauna suit and the last twenty minutes staring at a wall is allowed a sip of water. Tomorrow night he will weigh 170. His opponent will weigh 172. Both of them will be announced as lightweights, and neither of them will have been one for more than about a minute.

The short answer: the Unified Rules of MMA list fourteen named divisions from 105 lb to 265 lb plus a super heavyweight, the UFC uses eight of them for men and three or four for women, ONE Championship uses its own ladder because its fighters are not allowed to dehydrate, and the amateur federation IMMAF runs the same limits as the professionals with a few more at the edges. I will give you the numbers in both units, then the parts the numbers do not tell you: the weigh-in, the missed-weight penalties and how to pick a class you can actually make.

Key facts

Unified Rules divisions

14 named classes, 105 lb (47.6 kg) to 265 lb (120.2 kg), plus super heavyweight

UFC uses

8 men's divisions (125–265 lb), 3–4 women's (115–145 lb)

Allowance

1 lb (0.45 kg) for non-title fights; none for title fights

ONE Championship

10 divisions from 52.2 kg to 120.2 kg, walking weight plus hydration test, no weight cutting

IMMAF amateur

Same ladder as the professionals plus super heavyweight; women from 47.6 kg to 70.3 kg

Weigh-in

Day before the fight, roughly 24–36 hours out (ONE: during fight week)

The Unified Rules list, and what the UFC actually uses

The Unified Rules were written in New Jersey in 2000 with nine divisions, and in 2017 the Association of Boxing Commissions added five more in the gaps. The full ladder is below; the two right-hand columns are what matters if you watch the UFC.

Division	Limit (lb)	Limit (kg)	UFC men	UFC women
Atomweight	105	47.6	–	–
Strawweight	115	52.2	–	Yes
Flyweight	125	56.7	Yes	Yes
Bantamweight	135	61.2	Yes	Yes
Featherweight	145	65.8	Yes	Dormant since 2023
Lightweight	155	70.3	Yes	–
Super lightweight	165	74.8	–	–
Welterweight	170	77.1	Yes	–
Super welterweight	175	79.4	–	–
Middleweight	185	83.9	Yes	–
Super middleweight	195	88.5	–	–
Light heavyweight	205	93.0	Yes	–
Cruiserweight	225	102.1	–	–
Heavyweight	265	120.2	Yes	–
Super heavyweight	over 265	over 120.2	–	–

The ABC added atomweight, super lightweight, super welterweight, super middleweight and cruiserweight in 2017 so that promotions could close the 15- and 20-pound gaps that make some cuts brutal. The UFC has never used any of them. Its men still jump from 155 to 170 and from 205 to 265, which is why its heavyweight division contains people who weigh 107 kg and people who weigh 120, and why a lightweight who cannot make 155 any more has a very long way up to 170. The UFC’s women fight at strawweight, flyweight and bantamweight; a women’s featherweight division existed from 2017 and has been all but dormant since Amanda Nunes retired in 2023.

The allowance is the detail that the scale scene at the top turns on. For a non-title fight a fighter may weigh up to one pound over the limit, so 156 is a lightweight. For a title fight there is no allowance at all: 155.0 or nothing. Under the Unified Rules the limits are written in pounds; the kilogram figures above are conversions, and a commission that works in kilograms will publish its own rounded version.

ONE Championship: fight at the weight you are

In December 2015 the Chinese flyweight Yang Jian Bing died in Manila from complications of a weight cut before a ONE Championship card. Within weeks ONE abolished the practice. Fighters may not cut weight by dehydration at all: they declare a walking weight, they are weighed and hydration-tested during fight week rather than 24 hours before, a urine specific gravity above 1.0250 is a failed test, and intravenous rehydration is banned. Fail the test or the weight and you move up a division; a catchweight may not exceed 105 per cent of the lower division’s limit.

Because nobody is dehydrating, ONE’s limits sit roughly one division higher than the UFC’s, and the names moved with them.

ONE division	Limit (kg)	Limit (lb)	Same limit in the UFC
Atomweight	52.2	115	Strawweight
Strawweight	56.7	125	Flyweight
Flyweight	61.2	135	Bantamweight
Bantamweight	65.8	145	Featherweight
Featherweight	70.3	155	Lightweight
Lightweight	77.1	170	Welterweight
Welterweight	83.9	185	Middleweight
Middleweight	93.0	205	Light heavyweight
Light heavyweight	102.1	225	Cruiserweight (ABC only)
Heavyweight	120.2	265	Heavyweight

So a ONE lightweight and a UFC welterweight step on the scale at the same number. The difference is that the ONE fighter is still that weight when the bell rings. Fighters who move between the two promotions usually go down a name and stay the same size, which is confusing for fans and, from what they say, considerably better for the fighters.

IMMAF and the amateur game

IMMAF, the international federation for amateur MMA, runs the same ladder as the Unified Rules for men, strawweight 52.2 kg (115 lb) up to heavyweight 120.2 kg (265 lb), and adds a super heavyweight class above it. Women compete from atomweight 47.6 kg (105 lb) through strawweight, flyweight, bantamweight and featherweight to lightweight 70.3 kg (155 lb). IMMAF has adjusted its divisions between championships, so check the current handbook before you enter. Amateur fights are three rounds of three minutes with heavier gloves and shin guards, which is covered in MMA Rules Explained.

National amateur bodies and regional shows often use their own tables, sometimes in kilograms and with their own tolerance, and many weigh in on the day, which leaves no time to rehydrate. Fight at the weight you train at.

The weigh-in and the 24-hour problem

The Unified Rules do not say when the weigh-in happens; the commission does, and the practice almost everywhere is the day before the fight, roughly 24 to 36 hours before the walk. The UFC moved its official weigh-in to early morning in 2016, with a staged one in the afternoon. Those hours are the whole reason weight cutting exists. A fighter who can lose six or seven kilograms of water in the last two days and put it back overnight gets to fight someone smaller, and everyone in the division has to do the same or give that away.

The cost is well documented: worse endurance, slower reactions, a brain that tolerates a punch less well, and in the worst cases hospital visits and, as at ONE in 2015, deaths. California’s commission introduced a plan in 2017 that weighs fighters again on fight night and recommends moving up a class for anyone who has regained more than ten per cent. The physiology and a sane plan for a small cut are in Weight Cut Basics; what to drink between the scale and the first bell is in Hydration on Fight Day.

Missing weight and catchweights

When a fighter misses weight, three things happen in sequence. The commission asks whether the opponent will accept the fight anyway. If yes, it goes ahead as a catchweight, meaning at whatever the two of them now weigh, and the fighter who missed forfeits a share of the purse to the one who did not; in the UFC that share is commonly 20 to 30 per cent, though the commission and the promotion set it case by case. If the fight was for a title, only the fighter who made weight can win the belt, and a champion who misses is stripped on the spot.

A catchweight can also be agreed in advance: two fighters on either side of one of the UFC’s wide gaps contract a fight at, say, 160 lb. It counts on the record and settles nothing about a division, which is usually the point.

How to choose a class

Start from your walking weight: what you weigh in the morning, during a normal training week, eating like an adult. That number is your honest size. Then find the limit on the ladder that sits a few kilograms below it. For a professional under the Unified Rules that gap can be five to eight per cent with a well-managed cut and a day to recover; for an amateur with a same-day weigh-in it should be near zero. If two limits are equally close, take the higher one for your first few fights; the fighter you are worried about up there is exactly as worried about you.

Then leave it alone. Weight classes reward fighters who live near the limit year round, not the ones who visit it in fight week. Boxing has the same argument with seventeen divisions instead of fourteen: Boxing Weight Classes Explained.

Sources

• Unified Rules of Mixed Martial Arts, Association of Boxing Commissions and Combative Sports (abcboxing.com)
• Rules and Regulations: Unified Rules of Mixed Martial Arts, UFC (ufc.com)
• Global Martial Arts Rule Set and weigh-in and hydration policy, ONE Championship (onefc.com)
• Unified Rules of Amateur Mixed Martial Arts, International Mixed Martial Arts Federation (immaf.org)
• “Mixed martial arts weight classes”, Wikipedia

Where to go next

• The rest of the rule book, from the grounded definition to point deductions: MMA Rules Explained.
• How a cut works and how small to keep it: Weight Cut Basics and Hydration on Fight Day.
• The sport that invented weight classes: Boxing Weight Classes Explained and Boxing vs MMA.
• Where the divisions came from: History of MMA.
• The MMA hub.