I know it would really depend on the photo
That's it in a nutshell.
Plus it depends on your taste.
What I have found is that for my eyes, files often have to be slightly blurred in places and and sharpened in others to make them look believable. You really need to choose your paper (it makes a difference) and then print and look, and get a second opinion if possible and print again and again until you get a feeling for the image type, paper and print size combination.
Furthermore, if you have been sharpening for the web your prints will probably end up over-sharpened. The level of detail visible in 17” wide prints and larger can be horrifying.
Tiny flaws suddenly become huge.
Then there is your output sharpening. I'm lazy and automate it. I find Lightroom's “standard” setting good for most images, but I may not use it for say, fog. Qimage's default of “5” I find way too much.
Sorry I can't give you a formula.
Edit: You may also find that for prints you may need to check your capture sharpening. It needs a delicate hand. I found that earlier versions of Lightroom could cause nasty halos on on high contrast edges, particularly if there also had been some chromatic aberration, which wasn't noticeable for web use. For prints I would export two versions: one with and one without capture sharpening and layer them in Photoshop and brush in the capture sharpening on the main subject matter, avoiding the edges.