I used 1 in 12000 odds for calculating my numbers, which is based on following excerpt:
"But as close to an official source as exists on this topic is Golf Digest. That publication has provided "acer odds" since the 1950s, and in the year 2000 hired Francis Scheid, Ph.D., the retired chairman of the math department at Boston University, to calculate the odds using the latest and best information available.
The odds Scheid came up with were lower than any others cited above: 5,000 to 1 for a "low-handicapper," 12,000 to 1 for an "average player." If you are a low-handicapper and play 1,000 rounds in your life, according to Scheid, you have a 20-percent chance of recording an ace. If you play 5,000 rounds, your odds are 1:1."