What's the deal?

FOV in source engine is "fun", because like almost all engines with Quake heritage, aspect ratio correction is done by scaling the horizontal FOV to keep the vertical FOV intact (as is in a 4:3 screen). This puts people with the same FOV but wider screens than others at an advantage.

This isn't something that needs any new experimentation or evidence; it's a determined truth that people argue about even though it's been proven a million times before and always behaves exactly the same way.

If you're interested in the math, just read the javascript at the top of this page's HTML.

What's my real FOV?

FOV setting:
Display aspect ratio: :
Actual FOV:

What should I set it to for X real FOV?

Desired FOV:
Display aspect ratio: :
Respective Setting:
Note that source engine games usually cheat restrict their FoV settings to lie in a limited range, eg TF2's is 75-90.