I need help understanding all in one radiator classifications

[Sprung]

They all seem to be sold as sizes in increments such as 240, 280, 360 ect... Cases that I am looking at also indicate compatibility top/front/bottom via these classifications. My confusion lies in if you look at any given 280, its not going to be 280 mm long. Its going to most likely be longer than that. How can I know what will actually fit? For instance looking at this case (Fractal Air Pop XL):

It claims a top maximum size of 280. Does that mean 280 in general with some wiggle room or a 280mm hard limit?

Consider these two coolers:

Kraken Z63 RGB - 280mm Liquid Cooler listed, Dimensions:143 x 315 x 30mm per their tech sheet
Kraken Z53 RGB - 240mm Liquid Cooler listed, Dimensions:123 x 275 x 30mm per their tech sheet

It would seem to me that the 240 is the actual 280 and the 280 is closer to a 320 which is not a real classification.

What is your experience with these types of categories and measurements?

I really don't want to order stuff that won't fit.

 

[TheSlySyl]

Usually it means 280mm + whatever the added length for the connectors is. Fractal is usually very good at making sure that whatever it says fits, will fit.

 

[NattyKathy]

Rad length is always a "size class" based on fan quantity and dimensions. So 240mm = any radiator with 2x 120mm fans, 280 = a rad with 2x 140mm fans, 360 = 3x 120mm etc.
The exact dimensions differ slightly but for case fitment purposes the important part is how many fan "spaces" the rad takes up and cases are designed with a little wiggle room to account for radiator variation.

 

[lopoetve]

Same for using something like the ek mapping tools - it's good about "this will fit your case".