Depending on your Coding Culture, you order them based on "priority" (FATAL would have priority over all others, and therefore numbered as 1), or "importance" (FATAL would be most important, and therefore numbered 5.)

Alternatively, each is a flag in a number so that they can be combined, with FATAL being 1 or 16 depending on priority vs. importance.

I would argue that the names do indeed suffice to tell you their "level" - TRACE is the noisiest, least important, least priority level. DEBUG is next, followed by INFO, WARN, ERROR, FATAL.