Probability Calculator
Work out the probability of a single event from the number of favourable outcomes and the total possible outcomes.
Your results
Calculation breakdown
- Probability
- P(event) = favourable outcomes / total possible outcomes
Worked example
Drawing a heart from a standard 52-card deck has 13 favourable outcomes out of 52 total, giving a probability of 13/52 = 25%.
Assumptions
- Assumes all outcomes are equally likely (classical probability), which suits dice, cards and simple draws.
- Not suitable for conditional or dependent-event probabilities without adjustment.
How this calculator works
Enter the number of favourable outcomes and the total number of possible outcomes for an event with equally likely outcomes. The calculator returns the probability as a percentage, fraction and odds.
Frequently asked questions
What kind of events does this suit?
It suits classical probability problems with equally likely outcomes, such as drawing cards, rolling dice or picking from a bag.
Can I use this for combined or conditional events?
No, this basic calculator handles a single simple event; combined or conditional probabilities need a different formula.
What does '1 : 3 odds' mean?
It means for every 1 favourable outcome there are 3 unfavourable outcomes, an alternative way of expressing the same probability.