system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: how did the sizes of mattresses become standardized? Is there a regulation authority for such things?
gpt
There is no standard, it’s cultivated from years and years of different companies selling different products.

For example, if a mattress manufacturer’s 60x80” mattress (Queen) sells very well, the company that manufactures bed frames will want to sell frames that fit this size, as well as the company that sells sheets, comforters, etc. Concurrently, competitors also see this size selling well, so they will want to produce it themselves to capture some of that market.

That being said, there is still some variation in the market; one company’s King may measure 76x80” while the next company’s measures 78x80”.

I believe someone else in this thread pointed out the wiki page for bed sizes, you will see some variation between the popular sizes between different countries, all stemming from the above.