The formula
Multiply each value by its weight, add those products, then divide by the total of the weights.
The plain average is the same sum divided by how many values there are, which is the same as giving every value a weight of 1.
Worked example
Values 85, 90 and 78 with weights 2, 3 and 5 give 170 + 270 + 390 = 830. The weights total 10, so the weighted average is 83.
The plain average is 84.3333, so weighting towards the lowest value pulled the answer down by 1.3333.
When to use it
Use a weighted average when the values are not equally important: a final exam worth half the grade, or a price paid for different quantities.
If every value matters equally, the plain average is the right answer and the weighted version gives the same number with equal weights.
Inputs for the weighted average calculator
Values
The numbers being averaged, in any order, separated by commas or spaces.
Weights
How much each value counts, in the same order as the values. A weight of 5 counts five times as much as 1.
CALCULATOR QUESTIONS
Weighted average calculator questions
How do I calculate a weighted average?
Multiply each value by its weight, add the results, then divide by the total weight.
What if the weights add up to 1?
Then the weighted average is simply the sum of value times weight, because dividing by 1 changes nothing.
Do the values and weights have to be the same length?
Yes. Each value needs exactly one weight, and the calculator says so if the counts differ.
Can a weight be zero?
Yes. A weight of zero means that value does not count towards the average at all.