Weighted Average Calculator
Values and weights in — the weighted mean and each row's pull, live.
How this is calculated
weighted average = Σ(value × weight) ÷ Σ(weights)
Worked example (the defaults above): 80 × 30 + 90 × 50 + 70 × 20 = 2,400 + 4,500 + 1,400 = 8,300, divided by the total weight of 100, gives 83. The plain mean of the same three values is 80 — the difference is the 50-weight item dragging the answer toward 90, which is precisely what weighting is for.
Grades, portfolios, and honest weighting
The classic use is a course grade: each assessment's score weighted by its share of the final mark. The same math prices a portfolio's average return (weights = position sizes) and a blended cost of goods (weights = quantities). One honesty rule carries across all of them: weights must mean the same thing on every row — mixing percentage weights with quantity weights in one list produces a number that looks precise and means nothing.
Frequently asked questions
How is a weighted average calculated?
Multiply each value by its weight, add those products up, and divide by the sum of the weights: Σ(value × weight) ÷ Σ(weights). This page does it live for every row you fill in, and shows each row's contribution so you can see what is pulling the average where.
Do the weights have to add up to 100?
No — weights are normalized by their own total, so 30/50/20, 0.3/0.5/0.2, and 3/5/2 all produce the identical answer. Use whatever numbers your course outline or spreadsheet gives you.
How do I work out my course grade?
Enter each assessment's score as the value and its percentage of the final grade as the weight — e.g. assignments 80 at weight 30, project 90 at weight 50, exam 70 at weight 20 gives a course grade of 83. Rows you leave empty are simply ignored.
When is a weighted average the wrong tool?
When every item should count equally — that is the plain mean, one tab away in the average calculator. And for rates (like speeds over equal distances) the harmonic mean is the honest one; a weighted arithmetic mean of rates can mislead.