Muay Thai Weight Classes

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Let’s talk about Muay Thai weight classes. What are they? Why do we have weight classes? What are the different weight classes in Muay Thai? And how are weights checked for a fight?

What are Muay Thai Weight Classes?

Muay Thai Weight Classes are weight limits put in place so competitors will only be matched against opponents of similar weights. 

Muay Thai fights are always scheduled for a particular weight class so that no party stands to gain a weight advantage. 

Professional fighters usually weigh heavier than their weights at the time of the fights. They undergo a process known as a weight-cut in order to compete in the weight class. 

Purpose of Muay Thai Weight Classes
muay thai weight classes

There are several factors that affect striking power including precision, technique, and the force delivered.

All things equal and considered, an increase in mass will lead to an increase in force. This is the famous Newton’s Second Law of Motion (force is equal to mass multiplied by acceleration). 

This implies that a fighter will generate more striking power as he goes up in (lean muscle or just fat) weight. A kickboxer can deliver more impact with a heavier lean body mass (muscle) against an opponent of a lighter weight. 

Size mismatches are disadvantageous and dangerous for the smaller fighter in combat sports. Weight classes are implemented for safety reasons and to even the playing field by matching competitors of -or around – the same weight.

Every pound matters in the extremely competitive elite Muay Thai scene of Bangkok. Even a one-pound difference can sometimes be enough to skew the results between two prime athletes. 

More experienced fighters are given a weight disadvantage to make a fight more evenly-matched. This means that fighters compete at divisions that are above their optimal weight. 

A well-known example is the Muay Thai legend, Saenchai. He was often made to give up weight during his peak, and as many as over ten pounds when facing foreigners. 

Muay Thai Weight Classes

muay thai weight classes
Living legend, Saenchai at a weigh-in

There are many Muay Thai sanctioning bodies around the world. Weight division systems may differ among Muay Thai sanctioning bodies but usually with slight weight variations. 

However, weight classes of the same name can cover vastly different weights in different promotions. For those of you who are competing, it is important to check the exact weight limit with your promoter ahead of the weigh-in.

For the purpose of illustration, here are the Muay Thai weight classes adopted in the elite stadiums of Thailand (e.g. Lumpinee, Rajadamnern etc.) and the WBC Muay Thai (World Boxing Council):

  1. Mini Flyweight weight over 100 lbs but not exceeding 105 lbs. (47.629 kg.)
  2. Junior Flyweight weight over 105 lbs but not exceeding 108 lbs. (48.990 kg.)
  3. Flyweight weight over 108 lbs but not exceeding 112 lbs. (50.805 kg.)
  4. Junior Bantamweight weight over 112 lbs but not exceeding 115 lbs. (52.166 kg.)
  5. Bantam weight weight over 115 lbs but not exceeding 118 lbs. (53.526 kg.)
  6. Junior Featherweight weight over 118 lbs but not exceeding 122 lbs. (55.341 kg.)
  7. Feather weight weight over 122 lbs but not exceeding 126 lbs. (57.155 kg.)
  8. Junior Lightweight weight over 126 lbs but not exceeding 130 lbs. 58.971 kg.)
  9. Lightweight weight over 130 lbs but not exceeding 135 lbs. (61.238 kg.)
  10. Junior welterweight weight over 135 lbs but not exceeding 140 lbs. (63.506 kg.)
  11. Welterweight weight over 140 lbs but not exceeding 147 lbs. (66.681 kg.)
  12. Junior Middleweight weight over 147 lbs but not exceeding 156 lbs. (70.764 kg.)
  13. Middleweight weight over 156 lbs but not exceeding 160 lbs. (72.578 kg.)
  14. Junior Heavyweight weight over 160 lbs but not exceeding 175 lbs. (72.578 kg.)
  15. Heavyweight weight exceeding 175 lbs (79.383 kg.) and upwards.

Openweight Category

Fighters of different weights can actually compete against each other under the openweight category. However, this is not an official weight class for Muay Thai and the majority of combat sports.

UFC and MMA during the early years adopted the openweight concept with fights of dramatic weight difference. Those years were truly no-holds barred freakshows featuring weight differences over a hundred pounds.  

K-1 also featured a number of notorious openweight kickboxing fights including the memorable Kaoklai Kaennorsing vs Hong Man Choi clash. Check out some of Kaoklai’s highlights below:

Besides professional wrestling (i.e. WWE), Judo and Sumo are two martial arts sports with an openweight category. 

The most notable combat sport that continues to sanction openweight bouts is Lethwei. The Burmese boxing is one of the most brutal fight sports which allows headbutts. Lethwei is also typically fought in gauze and tape instead of padded gloves.

In openweight, the bigger, heavier and taller fighter enjoys a physical advantage but skills and fight fitness still play decisive factors. 

Cutting Weight & Weigh-Ins

cutting weight
Muay Thai legend, Singdam cutting weight in sauna suit

Cutting weight has become a tradition for Muay Thai like most other combat sports. 

Fighters undergo several days of severe weight-loss regime to meet the required weight during weigh-ins. Then they refuel and rehydrate to gain back a few pounds or kilograms. 

Weigh-ins are typically carried out the day before the actual event or the morning of the fight itself. This provides roughly about a 12- to 24-hr time frame for fighters to regain as much weight as possible. 

Cutting weight thus allows fighters to gain a weight advantage during the fight if done right, theoretically speaking. 

If a fighter fails to meet weight at the weigh-in, they may be allowed a few more hours to shed any excessive poundage. They usually go for a run on the treadmill in a sauna suit or head right to the sauna. 

Fights can be called off if a fighter fails to make weight. Sometimes, it is at the discretion of the promoter and the opponent who may accept the fight if it is not significantly over the weight limit.

The truth of the matter is that since everyone cuts weight and then regain after weigh-in, nobody actually gains any remarkable advantage.

Weight cuts can also lead to side effects like muscle loss, fatigue, nausea and stomach problems which affect performance in the ring.

Cutting weight has been a controversial topic for many years. The practice can be fatal due to the dehydration that takes place.  

For more about cutting weight, read this article: “Cutting Out Weight Cutting“.

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