This is not perfect, every gun is different, but is as good a guess as any. According to this website around 50 fps. I've not chronographed 9mm from anything but my 4" G-19 so I don't have any direct comparison with 9mm.
I have shot multiple barrel lengths in 44 mag and 357 mag handguns and several rifle calibers and have found their results with those calibers to be pretty accurate. Not perfect, but close
You also have to consder that each gun/barrel is different. It is not uncommon to see 50 or more fps difference between identical guns with identical barrel lengths firing ammo from the same box.