Probability Calculator

Probability Calculator Guide

Use this probability calculator to find the chance of an event as a decimal and percentage. It is designed for equally likely outcomes, plus common counting tasks such as combinations and permutations.

What Is Probability?

Probability measures how likely an event is to happen. A probability of 0 means impossible, 1 means certain, and 0.5 means a 50% chance.

Probability = favorable outcomes / total outcomes

How to Use This Calculator

1. Choose simple probability, combinations, or permutations.
2. Enter the values required for that mode.
3. Click Calculate.
4. Review the decimal, percentage, and working details.

Worked Examples

Example 1: A die has 6 sides. The chance of rolling a 4 is:

1 / 6 = 0.1667 = 16.67%

Example 2: A bag has 3 red balls and 7 total balls. The chance of choosing red is:

3 / 7 = 0.4286 = 42.86%

Example 3: Choosing 2 students from 5 without order uses combinations:

5C2 = 10

Mistakes to Avoid

Simple probability assumes outcomes are equally likely. If outcomes have different weights, use a weighted probability method instead. Also make sure favorable outcomes are not greater than total outcomes.

Important Note

This tool is best for introductory probability and counting problems. For advanced statistics, check whether your question requires independent events, conditional probability, or a binomial model.

Frequently Asked Questions

What is a favorable outcome?

A favorable outcome is the result you want to count, such as rolling a 6 on a die.

Can probability be greater than 1?

No. A valid probability is between 0 and 1, or between 0% and 100%.

What is the difference between combinations and permutations?

Combinations ignore order. Permutations count different orders separately.

When should I use this calculator?

Use it for simple chance questions, classroom examples, card/dice problems, combinations, and permutations.