I have a simple template I use for Tourny speed greens.
After I add/subtract elevation eg 16ft to pin, up2 in elevation 16+2=18ft
Always remember to hit slightly more. If you do the exact calculation, then the ball might come up short.
I use something similar, and it was based of 'Davesters' formula.
But I always tweak it after my trial and error. (lots of error)
I have to remember that greens can vary day to day as well, and the first or second putts will be an indication if a green is a little slower or faster than usual. That is party discussed in THIS thread, and likely already in this current one.
Again, like others I will take a 18 foot putt that goes up 2 inches = 20
Then 20 divided by approx. 1.37. (tourny) = 14.6
(lately this has been a little hard so you adjust your calculation, maybe 1.38+)
I usually hit a putt under 15 a little harder, to get the ball rolling.
But longer putts I shave off power because the ball is already rolling. One time I had to shave off about 11% off a 105 foot putt. I think it was a very fast green. But that's a whole new ball game. Generally, I remove power off the final solution as the distance becomes greater.
But Davester said that after you divide by 1.37 or 1.38 you add a foot of power for every 5 inches UP
or subtract a foot of power for every 5 inches down. (for inertia)
But it all varies so I just putt and pray like others have said. :D
This is from Davester's info but I think his webpage is gone, and I think the formula is not as accurate as it used to be, as things seem to always change, but it was a good starting point for me.