Understanding the odds and payoffs can be a little intimidating, but it's actually quite simple.
Win odds on the tote board are displayed based on $1, unless otherwise noted. A "3" displayed next to a horse's number indicates that the horse is 3-1. An example of an exception to this general rule is when "5-2" is shown. This simply means that the odds on this horse are actually 5 divided by 2, or 2.5-1.
Win payoffs are calculated based on a $2 wager because at most tracks this is the minimum bet.
A horse that wins at 3-1 will return $3 for every $1 wagered. For example, a $2 wager on a horse at 3-1 would return approximately $8:
$2 x 3 = $6 + $2 wagered = $8
Generally, when calculating a horse's win price, multiply two times the horse's odds and add $2. Notice that some odds pay through a range. Our horse with odds of 3-1 could pay anywhere from $8 to $8.80 in 20-cent increments. This occurs because the tote board can only display rounded odds.