The best formula out there IMO is this one from Young46, albeit very complicated, but if you put it into a spreadsheet it shouldn't be that bad.
IF elevation(in inches)(positive if uphill, negative if downhill) <0.4, elevation+0.35, IF NOT, elevation +1.35
Then multiply by 1.94
Divide by distance to the hole (in feet)
Then add the quotient of 17.9 / green speed(the number the game provides, on Championship 13 it would be 13, etc.)
Then divide by 2.25
Then multiply by the distance (in feet)
Lastly, add 1.1
I know it is complicated to hand calculate, but if you want to put it into a spreadsheet, the formula is as follows:
Cell B1 would be distance in feet
Cell B2 would be elevation in inches (remember positive for uphill and negative for downhill)
Cell B3 would be green speed #
Works on 99% of putts (Hint: generally take off a little bit when putting up more than 10 inches over a ridge)
Hope this helps!