How to Calculate Probability. Probability is the measure of how likely an event is to occur out of the number of possible outcomes. This wikiHow will show you. Definition. Probability means the chance or the likelihood of occurrence of an event. It is a numerical value that is lying between 0 and 1. When the event is. Convert A to B odds for winning or losing to probability percentage values for both winning and A:B Odds Probability Calculator Share this Calculation: help. Not Helpful 16 Helpful Featured Articles Probability and Statistics Games of Chance. Empirical or Statistical definition of probability Axiomatic definition of probability. Did you ever say something at exactly the same time as someone else? However, certain widely-circulated gambling strategies that at first appear to be "common sense" are, in fact, mathematically false.