Why is checked baggage usually limited to 23kg per bag?

Because of manual handling limits for baggage handlers, not aircraft weight — which is the reason it is a per-bag limit rather than a per-passenger total.

The health and safety basis. Baggage handlers lift thousands of bags per shift, often in confined aircraft holds, in awkward postures, at speed. Repetitive lifting is a leading cause of musculoskeletal injury in the industry, and back injuries among handlers have historically been a major source of lost working days and compensation claims.

The 23kg figure corresponds to roughly 50lb and aligns with widely used manual handling guidance about safe single-person lifts under realistic conditions. 32kg is the near-universal absolute maximum — above that, most airlines and airports will simply refuse the bag at any price, because handling regulations prohibit it. Bags between 23kg and 32kg are usually accepted with a heavy-bag fee and a warning label.

This explains something that otherwise seems arbitrary. If the limit were about aircraft weight, two 20kg bags and one 40kg bag would be equivalent. They are not: the 40kg bag is refused outright while 40kg split across two is fine. The constraint is the person lifting it.

Aircraft weight does matter separately, which is why total allowances exist, why airlines weigh passengers and cargo in aggregate, and why weight and balance calculations are performed for every flight — but that is a fleet-level concern, not the reason for the per-bag number.

Practical notes:

Allowances vary — 20kg, 23kg and piece-based systems all exist, and North American routes more often use a two-piece system.

Excess baggage charges are punitive at the airport and much cheaper purchased in advance.

Weigh at home. Bathroom scales holding the bag work well enough.

Airports increasingly automate handling, which may eventually change the rationale.