How to Calculate an Average

Step-by-step

1. List the values you want to include.
2. Add the values to find their sum.
3. Count how many values are in the list.
4. Divide the sum by the count.
5. Review the data for outliers or missing values that could affect the result.

Average formula

Arithmetic mean = sum of all values ÷ number of values. Make sure the count includes exactly the observations used in the sum.

Mean or median?

The mean can be affected by unusually large or small values. When data is skewed or contains outliers, compare it with the median before drawing conclusions.

Worked examples

For the scores 70, 85, 90 and 95, the sum is 340 and there are four scores, so the average is 85.

A weighted average gives some values more influence. If a score of 80 has weight 1 and a score of 90 has weight 3, the weighted average is (80 × 1 + 90 × 3) ÷ 4 = 87.5.