I have read this putting tip on my friends profile ( efratimike ) and is also in the forums.
This is much easier:
Very Fast greens - Hit 7.7 feet for every 10 feet of distnace
Tournament greens: Hit 8.7 feet for every 10 feet of distance
You can also quickly measure out the distance of a putt by simply using the calculator in windows.
29 feet 3+ inches - 32 feet
Or .85 multiplied by 7.7 = 27.2 feet