Everyday Math · 6 minute read

How to calculate a weighted average

Calculate grades, scores, or averages when some values count more than others.

Quick answer: Multiply each value by its weight, add those results, and divide by the total of the weights. If the weights are percentages that add to 100%, add the weighted results directly.

Why a regular average can be wrong

A simple average treats every value equally. A weighted average gives more influence to values that count more. This is common with course grades, investment returns, survey results, and average purchase prices.

If an exam counts for 60% of a grade and homework counts for 40%, the exam score should affect the final result more than the homework score.

The weighted-average formula

Multiply each value by its matching weight. Add all of those products. If the weights do not already equal 1 or 100%, divide the sum by the total weight.

Weighted average = sum of (value × weight) ÷ sum of weights

Example using grade percentages

Suppose homework is 90 and counts for 40%, while an exam is 80 and counts for 60%. Multiply 90 by 0.40 to get 36. Multiply 80 by 0.60 to get 48. Add them to get a final weighted score of 84.

The ordinary average would be 85, which is slightly too high because it gives the stronger homework score the same influence as the more important exam.

Example when weights are quantities

Imagine buying 10 items at $4 each and 30 items at $6 each. Multiply each price by its quantity: $40 and $180. Add them to get $220, then divide by 40 total items. The weighted average price is $5.50 per item.

Keep every weight in the same format.
Check that percentage weights add to 100%.
Do not average averages unless you also know their sample sizes.
Round only the final result when possible.

Frequently asked questions

Do weighted percentages have to add to 100%?

For a complete percentage-based average, yes. If they do not, divide by the total weight or check whether a category is missing.

What is the difference between an average and a weighted average?

A regular average treats values equally; a weighted average lets some values count more.

Can I average two class averages together?

Only if both groups contain the same number of items. Otherwise, weight each average by its group size.

Want help with the calculation?

Use the percentage calculator →

Published August 3, 2026 · Reviewed for clarity and source accuracy.