DIY Cost Tools
Weighted Average Calculator
Calculate a weighted mean from matching lists of values and nonnegative weights. The prefilled example shows a useful result immediately.
Enter 1 to 1,000 values and the same number of weights. Use commas or spaces. Weights must be nonnegative, with at least one positive. Individual magnitudes may not exceed 1 trillion.
How to use
Enter the required numbers, then select Calculate. Invalid inputs clear previous results and show an explanation. Answers display up to ten significant digits unless an exact integer factorization is shown. Match each value to its weight by position, and use a dot for decimal numbers.
Formula and explanation
Weighted average = Σ(wᵢxᵢ)/Σwᵢ. Each value xᵢ contributes in proportion to its weight wᵢ. Weights need not add to 100 because the calculator divides by their total. A zero weight removes that value’s contribution.
Worked example
Values 80, 90, 70 with weights 20, 50, 30 give (1,600 + 4,500 + 2,100)/100 = 82.
Important limitations
Assumes weights reflect the intended importance or frequency and correspond to values in the same order. Does not model missing-grade policies, dropped scores, or category rules. Negative weights are excluded. Use dots for decimals and omit thousands separators. Outputs are rounded floating-point estimates.
Frequently asked questions
Do weights have to total 100?
No. Proportional weights such as 2, 5, 3 give the same result as 20, 50, 30.
Can a value be negative?
Yes. Weights must remain nonnegative.
What if all weights are zero?
The average is undefined, so the tool rejects the input.
What if weights are equal?
The result equals the ordinary arithmetic mean.
Review notes
Reviewed October 1, 2026. Default outputs and boundary cases were independently checked. Blank, nonfinite, excessive, and calculator-specific invalid inputs were tested before publication. This is an educational tool; verify precision and domain assumptions for professional use.