How much sperm is in pre cum.?

Pre cum. Pre cum is fluid produced by the prostate gland during the early phase of sexual arousal. There are usually some spermatozoa present as the body is getting ready to eject a large concentrated volume of sperm soon afterwards.
Variable. Most studies have shown low levels of sperm or no sperm in pre-ejaculate with sperm not being motile (however, don't know how promptly samples were examined). One small study published in 2011 showed that there are some individuals with a high motile sperm count in pre-ejaculate. See: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3564677/