Grades and course credits
Combine subject marks, assessments or grade points where courses and assignments carry different credits or percentages.
Calculator Pro
Weighted Average Calculator
Calculate a weighted mean from any number of values and weights. Review every contribution, compare it with the simple average, and load practical examples for grades, inventory, procurement and investments.
Free to useCalculation shownDynamic rowsBrowser-based
Enter values and weights
Weights can be quantities, credits, percentages, investment amounts or any relative importance.
| Item | Value / score | Weight | Contribution | Action |
|---|---|---|---|---|
| 44.444444% | ||||
| 33.333333% | ||||
| 22.222222% |
Weighted average
85.555556
Weighted total
770
Total weight
9
Simple average
85
Difference from simple average
+0.555556
Highest value
90
Lowest value
80
Rows included
3
| Item | Value | Weight | Value × weight | Weight share |
|---|---|---|---|---|
| Mathematics | 90 | 4 | 360 | 44.444444% |
| Science | 80 | 3 | 240 | 33.333333% |
| English | 85 | 2 | 170 | 22.222222% |
| Total | 9 | 770 | 100% |
Calculation: 770 ÷ 9 = 85.555556. Weights do not need to total 100 because the weighted sum is divided by the actual total weight.
Understand the result
Weighted average formula
A weighted average is appropriate when the values do not contribute equally. A larger weight gives a value more influence over the final result.
Formula
Weighted average = Σ(value × weight) ÷ Σ(weight)
First calculate each value multiplied by its weight. Add those products to obtain the weighted total, add all weights, and divide the weighted total by the total weight.
- Σ means add all items
- Value is the score, price, rate or measurement
- Weight is quantity, credit, percentage or importance
- The denominator normalises weights automatically
Practical uses
Where weighted averages are used
The same formula supports educational, financial and operational decisions. The meaning of the value and weight changes, but the underlying calculation remains consistent.
Inventory average cost
Calculate an average unit cost from purchases made at different prices and quantities for ERP, POS and stock valuation workflows.
Supplier evaluation
Blend quality, delivery, price, service and compliance scores according to procurement priorities.
Investment portfolios
Calculate a portfolio return where each asset return is weighted by the amount invested or its portfolio allocation.
Employee performance
Combine KPI scores using approved organisational weights for quality, productivity, attendance or customer outcomes.
Quality and manufacturing
Summarise defect rates, test scores, batch measurements or production metrics when sample sizes differ.
Worked examples
Weighted average examples with answers
Use these examples to identify which column should contain the value and which should contain the weight.
Grade example
Scores of 90, 80 and 85 have course-credit weights of 4, 3 and 2. The weighted sum is 770 and the total weight is 9.
Result: 770 ÷ 9 = 85.56
Inventory cost example
Buy 100 units at 50, 150 units at 60 and 80 units at 55. Multiply every unit cost by its quantity, then divide by all 330 units.
Result: 18,400 ÷ 330 = 55.76 per unit
Supplier score example
Quality scores 95 with 50% weight, delivery scores 80 with 30%, and price scores 90 with 20%.
Result: (95×50 + 80×30 + 90×20) ÷ 100 = 89.5
Portfolio return example
Returns of 12%, 8% and 10% apply to investments of 20,000, 50,000 and 30,000 respectively.
Result: Weighted portfolio return = 9.4%
Comparison
Weighted average vs simple average
Choose the method according to whether each observation should have equal influence.
| Question | Simple average | Weighted average |
|---|---|---|
| How values are treated | Every value has equal importance. | Influence changes according to each weight. |
| Typical formula | Sum of values ÷ number of values | Sum of value × weight ÷ sum of weights |
| Best for | Values with equal relevance or equal sample sizes. | Grades, quantities, portfolios, scoring models and unequal sample sizes. |
| Example | Average of three monthly prices. | Average inventory cost when purchase quantities differ. |
Step by step
How to calculate a weighted average manually
1. List the values
Write every score, price, return or measurement in the value column.
2. Assign the weights
Enter the related quantity, credit, allocation or approved importance for each value.
3. Multiply value by weight
Calculate the weighted contribution for every row.
4. Add the contributions
The total of all products is the weighted sum.
5. Add all weights
Use the real total; the weights do not need to add to 100.
6. Divide
Weighted sum divided by total weight gives the weighted average.
Avoid errors
Common weighted-average mistakes
Dividing by the number of rows
A weighted average is divided by the sum of weights, not by the number of values.
Reversing value and weight
For inventory, unit cost is the value and quantity is the weight. Reversing them changes the meaning.
Mixing incompatible units
Use one consistent scale for all values and one consistent meaning for all weights.
Assuming weights must total 100
Credits and quantities rarely total 100. Normalisation occurs automatically through division by total weight.
Using a simple average for unequal quantities
A simple average of purchase prices ignores how many units were bought at each price.
Ignoring an organisation's official rules
GPA, performance and supplier models may include rounding, thresholds or conversion rules beyond a basic weighted mean.
Questions
Frequently asked questions
How is a weighted average calculated?
Multiply each value by its weight, add all of those products, and divide the weighted total by the sum of the weights. The calculator shows every contribution and the final division.
Do weights have to add up to 100?
No. Weights may be percentages, quantities, credits, investment amounts or relative scoring factors. Dividing by the total weight automatically normalises them.
Can this calculate weighted average inventory cost?
Yes. Enter each purchase price or unit cost as the value and the corresponding purchased quantity as the weight. The result is the weighted average unit cost across those quantities.
Can I use the calculator for grades?
Yes. Enter each grade as the value and its course credit or assessment percentage as the weight. Confirm whether your school uses a percentage score, grade points or a separate GPA conversion scale.
What happens when a weight is zero?
A zero-weight item contributes nothing to the weighted total and does not change the result. It can remain in the table for reference, although removing it makes the calculation easier to read.
What is the difference between a weighted average and a simple average?
A simple average gives every value equal influence. A weighted average gives more influence to values with larger quantities, credits, percentages or importance.
Can weights be decimals?
Yes. Decimal weights such as 0.4, 0.35 and 0.25 work in the same way as 40, 35 and 25 because the formula divides by the total weight.
Can I use negative values?
The mathematics supports negative values, which can be useful for returns or changes. Negative weights are usually not meaningful for grades, quantities or scoring and should be used only when your model explicitly requires them.
Is weighted average the same as weighted percentage?
A weighted percentage is a weighted average where the values or the final result are expressed as percentages. The calculation method is the same.
Does this calculator store my data?
The calculation runs in your browser. Avoid entering confidential business information on any shared device, and clear or reset the table after use when necessary.
Continue calculating
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