Weighted Average Calculator

A weighted average counts some values more than others: exam marks worth 40% of a grade, prices paid for different quantities, or survey groups of different sizes. This calculator takes value and weight pairs, one per line, and returns the weighted mean together with each item's share of the result and the ordinary average for comparison. Weights can be percentages, credit hours or any other numbers.

How to use this tool

1. Type one item per line: a value and its weight, optionally with a label first ("Final exam, 88, 40%").
2. Use percentages or plain numbers for the weights; they do not have to add up to 100.
3. Paste two columns straight from a spreadsheet if you prefer: tabs work as separators.
4. Read the weighted average and check which items pull it up or down in the table.

Formula

Weighted average = Σ(wᵢ × xᵢ) ÷ Σwᵢ

xᵢ are the values and wᵢ their weights. Dividing by the total weight means percentages that do not add to 100 still give a sensible result: the average of the work so far. Each item's contribution is wᵢxᵢ ÷ Σw, and the contributions add up to the weighted average.

Example

A course grade with homework 92 (20%), quizzes 85 (15%), midterm 78 (25%) and final 88 (40%): 92 × 0.20 + 85 × 0.15 + 78 × 0.25 + 88 × 0.40 = 18.4 + 12.75 + 19.5 + 35.2 = 85.85. The plain average of the four marks is 85.75, slightly lower because the strong final carries the most weight.