Golfindoog: way to calculate how it will affect your shot
Copy/Paste of one I put up in CC Forums a while back.
----------------------
How I handle the rough.
Disclaimer: A while back WGT added some VEM to rough. This was at the same time they messed with the wind, but that's another story. There will be instances where the rough has absolutely no effect. I find these more at RSG than anywhere else, but all courses have this. This is WGT's take on catching a flyer.
Generally add the appropriate percentage of distance to your calculations. This does not apply to Fescue, Brush or Mulch. Those are different. This applies to plain deep grass rough.
20/30 - 3%
25/30 - 7%
30/40 - 12%
40/50 - 23%
Worse than that? Just get back into play.
Hope this helps.