Weighted Average Calculator
Weighted Average Calculator multiplies each value by its matching weight, sums those products, and divides by the total weight. Values and weights must have the same number of entries. Weights can be counts, credits, proportions, or other importance measures, but their meaning must be consistent and their total cannot be zero.
Runs locally — files stay on your deviceWhat is the weighted average of 80 and 90 with weights 1 and 3?
The weighted average is 87.5.
Formula: (80×1 + 90×3) ÷ (1+3) = 87.5
Weights control each value's contribution
Weighted mean = Σ(value×weight) ÷ Σweight. Multiplying every weight by the same nonzero factor does not change the result.
How it works
Enter values and weights in matching order. Confirm what weights represent and check their total before interpreting the result.
Key concepts
Order pairs values with weights
The first weight belongs to the first value, and so on.
Relative weights matter
Weights 1,3 and 25,75 produce the same relative influence.
When to use it
- Average grades with different credits.
- Combine group means using group sizes.
- Calculate a blended rate from known weights.
When not to use it
- Do not mismatch value and weight order.
- Do not use weights that sum to zero.
- Do not assume percentages must sum to 100; any proportional scale works.
Worked examples
Course credits
- Input
Values 80,90; weights 1,3- Expected output
87.5
The second value has three quarters of the influence.
Group averages
- Input
Means 10,20; sizes 90,10- Expected output
11
A simple average of group means would incorrectly give fifteen.
Percentage weights
- Input
70,90 with 40,60- Expected output
82
Weights sum to one hundred but do not need percent symbols.
Common mistakes
Different list lengths
Some values have no matching weight. Correction: Provide one weight per value.
Averaging weighted products without dividing
The scale of weights remains in the result. Correction: Divide by total weight.
Using negative weights casually
The result can leave the observed range. Correction: Use domain-appropriate weight rules.
Best practices
- Label weight meaning.
- Verify list order and length.
- Check total weight and expected output range.
Related operations and differences
Average Calculator
Choose Average Calculator when you need to find the arithmetic mean of a number list.; use Weighted Average Calculator specifically for weighted average.
Fraction to Decimal
Choose Fraction to Decimal when you need to convert a numerator and denominator to decimal.; use Weighted Average Calculator specifically for weighted average.
Percentage Difference Calculator
Choose Percentage Difference Calculator when you need to compare two values by their average magnitude.; use Weighted Average Calculator specifically for weighted average.
Proportion Calculator
Choose Proportion Calculator when you need to solve A:B = C:X safely.; use Weighted Average Calculator specifically for weighted average.
Ratio Calculator
Choose Ratio Calculator when you need to calculate the ratio between two numbers.; use Weighted Average Calculator specifically for weighted average.
GPA Calculator
Choose GPA Calculator when you need to average a list of grades on a 0–4 scale.; use Weighted Average Calculator specifically for weighted average.
Limitations and privacy
- The page does not enforce domain-specific rules for negative weights.
- Values and weights must be finite matching lists.
- Total weight cannot be zero.
Numbers and results remain in this browser.
Frequently asked questions
Do weights need to total 100?
No. Only their relative values matter.
Why must list lengths match?
Each value needs exactly one corresponding weight.
What if all weights are equal?
The result equals the ordinary arithmetic mean.
Can total weight be zero?
No. The formula would require division by zero.