How to use this weighted average calculator
Enter your values in the first box and their weights in the second, in the same order. Weights can be percentages (40, 30, 30) or any plain numbers (4, 3, 3). The calculator divides by the total weight either way.
When a plain average lies
A plain mean assumes every value matters equally. Grades rarely work that way: a final exam worth 40% of a course should pull your average twice as hard as a quiz worth 20%. The weighted mean fixes the arithmetic by letting each value vote in proportion to its importance.
Course marks: coursework 78 (weight 40%), midterm 85 (30%), final project 92 (30%). Weighted: (78×40 + 85×30 + 92×30) ÷ 100 = 8430 ÷ 100 = 84.3. The plain mean of the three marks is 85, close but wrong in the direction that matters at a grade boundary, because it over-credits the lightly-weighted midterm and under-credits the heavy final project.
Where weighted averages run the world
GPA calculations (credits as weights), portfolio returns (position sizes), survey analysis (demographic weights), price indices like the CPI (household spending shares), anywhere some observations legitimately count more than others. If you ever catch yourself averaging group averages of different-sized groups, stop: that is a weighted mean waiting to be done properly.
Frequently asked questions
What is the difference between a weighted average and a regular average?
A regular average gives every value equal importance (weight 1). A weighted average multiplies each value by its weight first, so more important or larger items influence the result more.
Do weights have to add up to 100?
No. The calculator divides by the total weight, so 40/30/30, 4/3/3 and 0.4/0.3/0.3 all give the same answer.
How is GPA a weighted average?
Each course's grade points are weighted by its credit hours: a 4-credit A moves your GPA more than a 1-credit A.