Weighted Average Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/5/2026
The weighted average is calculated with Σ(value × weight) ÷ Σ(weight). For the values 15, 10, and 18 with weights 2, 1, and 3, the weighted average is about 15.67.
Explanation
Unlike a simple average, where each value counts as much as the others, a weighted average assigns each value a weight (also called a coefficient) that reflects its relative importance in the final result. This is the principle used, for example, to calculate a school average where certain subjects count double, or an average combining continuous assessment and a final exam with different weightings. Concretely, each value is multiplied by its weight, these products are added together, and the total is divided by the sum of the weights (not by the number of values, as with a simple average). When all the weights are equal, the weighted average gives back exactly the same result as a simple average. This calculator works with 3 fixed values; for a weighted average between just 2 components (an already-earned grade and a final exam, for example), see our percentage calculator, which can be used for that kind of two-component weighting; for a different way of summarizing a data set's spread, see our z-score calculator.
Example: three grades with different coefficients
Inputs
Value 1: 15 (weight 2). Value 2: 10 (weight 1). Value 3: 18 (weight 3).
Calculation
Weighted average = (15 × 2 + 10 × 1 + 18 × 3) ÷ (2 + 1 + 3) = (30 + 10 + 54) ÷ 6 = 94 ÷ 6 ≈ 15.67.
Result
The weighted average of the three values is about 15.67.
Frequently asked questions
Why isn't the result the same as a simple arithmetic average?
Because each value doesn't count the same way: the one assigned the highest weight (18, with a weight of 3 in the example) influences the final result more than the others. A simple average of the same three values (15+10+18)/3 would give 14.33, different from the 15.67 obtained with weighting.
What if I only have 2 values to weight?
Just leave one of the three weights at zero: the associated value will then have no influence on the result, which amounts to considering only the other two.
Do the weights have to add up to 100 or 1?
No, that's not necessary: the formula always divides by the actual sum of the weights entered, whatever that sum is. Weights of 2, 1, and 3 (total 6) give exactly the same result as weights of 20, 10, and 30 (total 60), since only the ratio between the weights matters.