Percentage average calculator
The calculator above multiplies two numbers, which is the step a weighted average needs: each percentage times its weight. Add those, divide by the total weight, and you have the answer.
12 × 12 = 144
Adding 12 to itself 12 times gives the same answer.
The plain average of percentages
- Add every percentage together.
- Divide by how many there are.
Four test scores of 80, 90, 70 and 100 add to 340. Divided by 4, the average is 85%. This is correct only when each percentage came from a group of the same size.
The weighted average
- Multiply each percentage by its weight, using the calculator above.
- Add all those products.
- Divide by the total of the weights.
An exam worth 70% at a score of 60, and coursework worth 30% at a score of 90: 60 x 70 = 4200, 90 x 30 = 2700. Together 6900, divided by 100, gives 69%.
The mistake that inflates the answer
Averaging percentages that came from different-sized groups. Say 50% of 10 people and 90% of 100 people. The plain average says 70%. The real figure is 5 plus 90 out of 110, which is 86.4%. The small group pulled far more weight than it deserved. Whenever the groups differ in size, weight by the size.
When the answer looks wrong
Your average must land between the smallest and the largest of your percentages. If it does not, a weight has been typed into the wrong box or a value has been counted twice. And if the total of your weights is not 100, divide by the real total, not by 100.
For a single percentage rather than an average, see how to find a percentage on a calculator. Grades have their own weighting on the GPA percentage calculator, and the full set is on calculators.