Weighted Average Calculator
Find the weighted average of values that count for different amounts.
About this tool
Multiplies each value by its weight, adds the results and divides by the total weight. Weights can be percentages, credits, quantities or any other numbers, and they do not need to add up to 100.
A normal average treats every number the same. A weighted average lets some count more than others: an exam worth 40% of your mark, a module with more credits, or shares you bought more of at one price. Enter each value with its weight, one pair per line, to get the weighted average, the total weight and the plain average for comparison.
How to use the Weighted Average Calculator
- Type one value and its weight per line, separated by a comma or space, for example 72, 40.
- Use any weights: percentages, credits or quantities. They do not have to add up to 100.
- Read the weighted average and the total weight.
- Compare it with the plain average underneath.
A final course mark
A course has three assessments: a test worth 40% where you scored 72, a project worth 25% where you scored 85 and an exam worth 35% where you scored 64. The weighted average is (72 × 40 + 85 × 25 + 64 × 35) ÷ 100 = (2 880 + 2 125 + 2 240) ÷ 100 = 72.45. The plain average of the three scores would be 73.67, which overstates the mark because the high project score counts for the least.
When to use a weighted average
Use a weighted average whenever items contribute unequally to a total. Course marks weight each assessment by its share of the grade. A GPA weights each grade by its credits. The average price paid for shares weights each purchase price by the number bought, and a price index weights each product by how much people spend on it. The formula is the same each time: sum of value × weight, divided by the sum of the weights. If all the weights are equal, the weighted average is the same as the plain average. A common mistake is averaging percentages that come from groups of different sizes; weight each by the size of its group instead.
Frequently asked questions
Do the weights have to add up to 100?
No. The calculator divides by the total weight, so 40, 25 and 35 give the same answer as 0.4, 0.25 and 0.35.
How do I work out my average share price?
Enter each purchase price as the value and the number of shares bought as the weight.
What is the difference between weighted and plain average?
A plain average gives every value equal importance. A weighted average gives each value importance in proportion to its weight.
Can weights be zero?
Yes, a value with weight 0 is ignored. At least one weight must be above zero.