How are machine guns classified as light, medium, or heavy?

Modern machine guns are categorized into three primary groups based on their operation, ammunition, and deployment:1

• Light Machine Guns (LMG): Also known as squad automatic weapons, these are designed to be operated by a single soldier and are typically equipped with a bipod. They generally use box-type magazines and are chambered for the same small-calibre, intermediate-power ammunition used by the assault rifles within their military unit.1
• Medium Machine Guns (MMG): Often referred to as general-purpose machine guns (GPMG), these are belt-fed weapons that can be mounted on either a bipod or a tripod. They are typically chambered for full-power rifle ammunition.21
• Heavy Machine Guns (HMG): Historically, this term referred to water-cooled, belt-fed weapons operated by a dedicated squad and mounted on a tripod. Since 1945, the classification has shifted to denote automatic weapons that fire ammunition larger than standard combat rifle rounds, most commonly .50 inch (12.7 mm) calibre.1