A Weighted Average Calculator
A weighted average answers "what is the typical value?" when some values count more than others. Grades, portfolio returns, inventory costs and survey results are almost never plain averages, which is why the distinction matters.
Weighted average
85.7
- Unweighted average for comparison
- 85
- Total weight
- 100
- Effect of the weights
- 0.7
Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.
The formula this calculator uses
Weighted Average = Sum of (Value x Weight) / Sum of Weights
- vi
- Each individual value
- wi
- The weight attached to that value
- Sum vi x wi
- Total of every weighted contribution
- Sum wi
- Total weight — 100 if you are already using percentages
How to check the result by hand
- 1
List each value with the weight it carries
Write them side by side so units are visible. If the weights are percentages summing to 100 the denominator simplifies to 100, otherwise add them explicitly.
- 2
Multiply each pair
85 x 30 = 2550, 92 x 40 = 3680, and 78 x 30 = 2340. Each product is that value's total contribution to the result.
- 3
Add both columns
Contributions total 8570 and weights total 100. Keeping the two sums separate is what prevents the classic mistake of dividing by the number of items instead.
- 4
Divide contributions by total weight
8570 / 100 = 85.70. Note this sits between 78 and 92, where any weighted average of those numbers must sit.
- 5
Compare against the plain average
(85 + 92 + 78) / 3 = 85.00. The 0.70 gap tells you the weights shifted the outcome toward the higher-weighted 92 — a helpful check that the answer moved in a sensible direction.
For worked examples, common mistakes and the limits of this formula, read the full How To Calculate A Weighted Average page.