It's actually called effective seat tube length.
Why do you keep quoting single number inch sizes as if we're still in the 1990s? You must be older than Jesus because it's been decades since even US manufacturers have quoted frame sizes that way. In the modern era you get a published geometry table, always in metric millimeters. The so called frame size is often just s/m/l/xl or some generic 1/2/3/4 scale, because your type of single number frame size quoting is dinosaur obsolete (for exactly the reason I attempted to teach you in my past several posts). We are well past the pre-historic era where most frames had similar geometries and a single seat tube number can be used for sizing.
Astounding lack of knowledge for someone who has the audacity to participate in this thread.
While bicycle companies use centimeters for road bikes, they still list frame sizes in cm. For example
the Specialized Tarmac SL8 Pro is listed in frame sizes of centimeters. Of course those are for a virtual seat tube length. The actual length of the seat tube is 380mm which isn’t close to 58cm. However, the rest of the geometries match a “58cm” frame. If that example isn’t enough, the
Allez is listed by frame size as is the
Roubaix and
Aethos. Electric bikes seem to be the outlier in the Specialized line.
It looks like Trek is using S, M, L, etc. as is Giant. But I’d bet if you walked into a dealer for either one and said you regularly ride, for example, a 58 cm bike, they would pull out a large for you to test.