Transparent method
The formula
Worked example
Example inputs
How to interpret the result
A weighted average only means what it's supposed to mean when the weights actually add up to a whole, 100%, or 1.0. Enter weights that sum to 80% or 120% by mistake, whether from a typo or from forgetting one category, and the result silently drifts away from a genuine average without throwing any error, because the arithmetic runs fine either way.
Before you rely on it
What to check
Add up all the entered weights before trusting the result. They should total 100% (or 1.0); anything else means the average is being computed against the wrong total.
The common error
Where people go wrong with weighted average calculator
Forgetting to include every category's weight, leaving the total below 100%. The calculator still returns a number, but it's a genuine average of a subset, not the intended weighted average of the whole.
Step by step
The worked example, input by input
| Input | Value used |
|---|---|
| Value 1 | 90 |
| Weight 1 | 0.3 |
| Value 2 | 80 |
| Weight 2 | 0.3 |
| Value 3 | 95 |
| Weight 3 | 0.4 |
| Weighted average | 89 |
| Sum of weights | 1 |
Where the inputs come from
Enter each value with its weight, the importance or share of that value. For a course grade the values are scores and the weights are the percentages each category counts, for example 30%, 30% and 40%. Weights can be percentages, decimals or counts such as credit hours, and they need not add to 100 because the calculator divides by their total. Make sure each weight matches the right value.
When the result stops applying
A weighted average can hide a wide spread, so two very different sets of values can give the same result. Weights must be non-negative, and a weight of zero removes a value. If a category is missing, the remaining weights should be renormalized. It is not the same as the mean of the averages when groups have different sizes.
What to compare it with
Compare with the simple mean on the mean and median calculator, and see the grade target calculator for what score you need. The GPA calculator is a weighted average by credit hours, and the portfolio weighted return page applies it to investments. The standard deviation calculator measures spread.
People also ask
Frequently asked questions
How is a weighted average different from a simple average?
A simple average treats every value equally, while a weighted average multiplies each value by its importance before dividing by the total weight.
Do weights have to add up to 100%?
No. The calculator divides by the sum of the weights, so any positive weights work, though percentages summing to 100 are easy to interpret.
Where are weighted averages used?
In grades, GPAs, index funds, portfolio returns, inventory costing and surveys, wherever some items count more than others.