Average Calculator

The average, also called the arithmetic mean, is a single number that represents the center of a data set. It is calculated by summing all values and dividing by the total count of values. For example, the average of 4, 8, 15, 16, 23, and 42 is (4+8+15+16+23+42) / 6 = 18. It is the most commonly used measure of central tendency in everyday math, statistics, and business reporting.

A simple average treats every value equally and divides the sum by the count of values. A weighted average assigns each value its own importance, or weight, so values with a higher weight influence the result more than values with a lower weight. The formula is Σ(value × weight) / Σ(weight). Weighted averages are used whenever some data points matter more than others, such as grades worth different credit hours or stock purchases made in different quantities.

First, list every number in your data set. Second, add all the numbers together to get the sum. Third, count how many numbers are in the set. Fourth, divide the sum by the count — the result is your average. For a weighted average, multiply each value by its weight first, add those products together, then divide by the sum of the weights instead of the plain count.

To calculate an average percentage from several percentage values, add all the percentages together and divide by how many there are, the same as a simple average. However, if each percentage comes from a different sample size (for example, test scores out of different total points), you should use a weighted average instead — multiply each percentage by its corresponding sample size, sum those products, and divide by the total sample size. This avoids overweighting percentages based on very small samples.

A class average is the mean score of every student on an assignment or exam, calculated by summing all scores and dividing by the number of students. A GPA calculation is a weighted average where each course grade is weighted by its credit hours, since a 4-credit course should count more toward your overall GPA than a 1-credit course. Both use the same underlying average formulas — the class average uses a simple mean, while GPA uses the weighted average method.

When you buy shares of the same stock at different prices and quantities over time, your average cost basis per share is a weighted average: multiply each purchase price by the number of shares bought at that price, sum those totals, and divide by the total number of shares owned. This gives a single blended price per share that is used to calculate gains or losses when you eventually sell, rather than tracking every individual purchase lot separately.