⚖️ Weighted Average Calculator
By ToolNimba Editorial Team · Updated 2026-06-19
This weighted average calculator works out the weighted mean of a set of values where each value carries a different importance, or weight. Enter each value with its weight, add as many rows as you need, and you will instantly see the weighted average, the total weight, and the plain simple average for comparison. It is ideal for course grades, survey scores, investment returns, and any figure where some numbers should count more than others.
What is the Weighted Average Calculator?
A weighted average (or weighted mean) is an average in which some values count more heavily than others. In an ordinary average every number has equal say, but in real life that is often wrong: a final exam worth 50% of a grade should not count the same as a quiz worth 5%. The weight is simply a number that says how much each value matters relative to the rest. Larger weights pull the result toward their value.
The calculation is straightforward. Multiply each value by its weight, add up all of those products, then divide by the sum of the weights. The division by total weight is what keeps the answer on the same scale as the original values. If every weight is the same, the weighted average collapses back to the ordinary simple average, which is a useful sanity check.
Weights do not have to add up to 100 or to 1. You can use raw counts (3 credits, 5 shares, 12 responses) or percentages, and the maths still works because dividing by the total weight normalises everything automatically. The one rule that cannot bend is that the total weight must be greater than zero. If every weight is zero there is nothing to divide by, and a weighted average is undefined.
When to use it
- Working out a course grade where assignments, quizzes, and the final exam each count for a different percentage.
- Combining survey ratings when each response represents a different number of people.
- Calculating a blended return across investments of different sizes in a portfolio.
- Averaging product review scores where some products have far more ratings than others.
- Setting a single cost figure from suppliers who shipped different quantities at different prices.
How to use the Weighted Average Calculator
- Type your first value into the Value box and its importance into the Weight box.
- Add a row for every value, giving each one its own weight.
- Use weights as percentages, credits, counts, or shares, whatever fits your data.
- Read off the weighted average, with the total weight and simple average shown alongside for comparison.
- Remove any row you do not need, or clear a weight to zero to drop a value from the weighting.
Formula & method
Worked examples
A course grade: homework 80 (weight 20%), midterm 75 (weight 30%), final 90 (weight 50%).
- products: 80 x 20 = 1600, 75 x 30 = 2250, 90 x 50 = 4500
- sum of products = 1600 + 2250 + 4500 = 8350
- total weight = 20 + 30 + 50 = 100
- weighted average = 8350 / 100 = 83.5
Result: Weighted grade = 83.5 (the simple average of 80, 75, 90 would be 81.67).
Blended price: 100 units at $2 and 300 units at $5.
- products: 2 x 100 = 200, 5 x 300 = 1500
- sum of products = 200 + 1500 = 1700
- total weight = 100 + 300 = 400
- weighted average = 1700 / 400 = 4.25
Result: Average price per unit = $4.25, pulled toward $5 because most units cost $5.
Weighted average versus simple average for the same values
| Values | Weights | Simple average | Weighted average |
|---|---|---|---|
| 80, 90 | 1, 1 | 85 | 85 |
| 80, 90 | 1, 3 | 85 | 87.5 |
| 80, 90 | 3, 1 | 85 | 82.5 |
| 60, 100 | 4, 1 | 80 | 68 |
Common sources of weights
| Context | Value | Typical weight |
|---|---|---|
| Course grade | Assignment score | Percent of final grade |
| Portfolio return | Asset return % | Amount invested |
| Survey result | Group rating | Number of respondents |
| Purchasing | Unit price | Quantity bought |
Common mistakes to avoid
- Confusing the weighted average with the simple average. A simple average treats every value equally. If your numbers differ in importance, the simple average will be wrong. Compare the two figures this tool shows to see how much the weighting moves the result.
- Forgetting that weights need not sum to 100. You can use raw counts like credits or quantities as weights. Dividing by the total weight normalises them automatically, so 3, 5, 2 works just as well as 30%, 50%, 20%.
- Leaving a total weight of zero. If every weight is zero there is nothing to divide by and the result is undefined. Give at least one value a weight above zero.
- Weighting the wrong number. The weight should describe how much each value matters, not the value itself. Putting the value in the weight column (or the reverse) silently produces a meaningless result.
Glossary
- Weighted average
- An average where each value is multiplied by a weight before being combined, so more important values count more.
- Weight
- A number that sets how much a value contributes to the average. Larger weights pull the result toward that value.
- Simple average (mean)
- The ordinary average: add all values and divide by how many there are, treating each value equally.
- Total weight
- The sum of every weight. The sum of value times weight is divided by this to get the weighted average.
Frequently asked questions
What is a weighted average?
A weighted average is an average in which some values count more than others. Each value is multiplied by a weight, the products are added, and the total is divided by the sum of the weights, so important values have more influence on the result.
How do I calculate a weighted average?
Multiply every value by its weight, add up all the products, then divide by the sum of the weights. For example (80 x 2 + 90 x 3) / (2 + 3) = 430 / 5 = 86. This calculator does all of that for you as you type.
How is it different from a normal average?
A normal (simple) average treats every value equally. A weighted average lets some values count more by giving them larger weights. When all weights are equal, the two give the same answer.
Do the weights have to add up to 100 or to 1?
No. You can use percentages, but raw counts such as credit hours, shares, or quantities work just as well. Dividing by the total weight normalises them, so the scale of the weights does not change the result.
How do I calculate a weighted grade average?
Enter each grade as a value and the percentage it is worth as the weight. For example homework 80 at 20%, midterm 75 at 30%, and final 90 at 50% gives a weighted grade of 83.5.
What happens if the total weight is zero?
A weighted average cannot be calculated when all weights are zero, because dividing by zero is undefined. The tool flags this and shows the simple average instead until you give at least one row a positive weight.