Average Percentage Calculator
Simple, or weighted by group size.
The calculator never sends or saves what you type.
On this page
How to calculate average percentage
Average percentage = Σ(% × size) ÷ Σ sizes
With no sizes, every size is 1 and this is the simple average. Worked example, for 80%, 65% and 90%:
- Add the percentages: 80 + 65 + 90 = 235.
- Divide by how many there are: 235 ÷ 3 ≈ 78.33%.
With sizes, the same three percentages from groups of 120, 40 and 200:
- Multiply each percentage by its group’s size: 80 × 120 = 9,600; 65 × 40 = 2,600; 90 × 200 = 18,000.
- Add the products: 30,200.
- Divide by the total size: 30,200 ÷ 360 ≈ 83.89%.
The calculator says which of the two it did in the answer itself, and beside a weighted average it shows the simple one too.
Simple vs weighted average percentage
Three classes take the same test. The pass rates are 80%, 65% and 90%, but the classes are not the same size:
| Class | Students | Pass rate | Passed |
|---|---|---|---|
| Class A | 120 | 80% | 96 |
| Class B | 40 | 65% | 26 |
| Class C | 200 | 90% | 180 |
| Total | 360 | 302 |
302 of 360 students passed: 83.89%. That is the weighted average, and it is the same as pooling every class into one. The simple average, 78.33%, treats the 40 students in Class B as if they counted as much as the 200 in Class C.
Starting from the counts instead? Add them up: type 96+26+180 as the marks and 360 as the total in the marks percentage calculator.
Only the proportions between the sizes matter: 120, 40 and 200 give 83.89%, and so do 12, 4 and 20 (83.89%). Shares of a whole work too — type them all with a % sign or all without.
When the simple average is right
When every group is the same size, the sizes cancel out: 80%, 65% and 90% of 50 people each average 78.33%, exactly the simple average. Pass rates of classes, survey results by region and conversion rates of campaigns with different traffic are the cases that need the sizes.
| Percentage | Weight it by |
|---|---|
| Pass rate | Students who sat the test |
| Survey share | Respondents |
| Conversion rate | Visitors |
| Defect or on-time rate | Units or deliveries |
| Exam percentage | Maximum marks |
| Attendance percentage | Classes held |
| Availability or uptime | Requests served, or minutes in the period |
The size is always the number the percentage was taken of.
Availability is the same case. Three months at 99.95%, 99.80% and 99.99% give the quarter’s figure when each is weighted by its requests, or by its minutes for a time-based target; the simple average is right only if every month carried the same traffic. What to promise, and what the gap to 100% buys you, is the error-budget conversation in OpsCanopy’s SLOs and alerting lesson.
Percentages over 100%
Growth indexes and targets beaten run over 100%, and they average the same way: 120%, 135% and 90% average 115.00%. An average always lies between the smallest and the largest value. This calculator takes percentages up to 10,000% and sizes up to 1,000,000, and it never rounds an average to 100% that is not exactly 100: 99.99% and 100% average 99.995%.
Average percentage in Excel and Google Sheets
For the simple average of A2:A4, use =AVERAGE(A2:A4). For the weighted average, with the sizes in B2:B4, use =SUMPRODUCT(A2:A4,B2:B4)/SUM(B2:B4). Dividing by the SUM of the sizes, not by how many there are, is what weights them. The same formulas work in Google Sheets. If you have the counts rather than the percentages, =SUM(C2:C4)/SUM(B2:B4), with the counts in C2:C4, gives the same overall rate.
Cells formatted as percentages hold fractions — 80% is stored as 0.8 — so the result is a fraction too, shown as a percentage by the same formatting. Typed here, 0.8 means 0.8%: the calculator notes it when every value is under 1.
When averaging percentages is wrong
Three cases, each with its fix. Groups of different sizes: weight by size, as above. Marks out of different totals: 80% of 50 and 60% of 100 are 66.67% overall, not 70.00% — add the marks and the totals, or weight each percentage by its total. Changes over time: +10% and then −10% leave 99% of the start, because each change applies to a different base. That is compounding, not an average, so this calculator takes no negative percentages. For the overall change, compare the start with the end in the percentage change calculator. An average yearly growth rate is a compound (geometric) rate, which this page does not calculate.
Grades and marks
For a course grade from weighted categories — homework, quizzes, a final — the weighted grade calculator also says how much of the course is graded so far. For marks out of a total, the marks percentage calculator adds them up for you.
Semester or subject percentages with different maximum marks: put each maximum in Sizes, which gives the same figure as adding the marks. Which semesters count is your university’s rule. For grade points, the SGPA to CGPA calculator does the credit-weighted average.
Frequently asked questions
Can you average percentages?
Yes, if every percentage comes from a group of the same size: then the simple average is right. If the groups differ in size, weight each percentage by its group’s size. Pass rates of 80%, 65% and 90% average 78.33%, but if the classes have 120, 40 and 200 students, the overall pass rate is 83.89%.
How do you find the average of percentages?
Add them and divide by how many there are: (80 + 65 + 90) ÷ 3 ≈ 78.33%. That is the simple average. For a weighted average, multiply each percentage by its group’s size, add the products and divide by the total size: (9,600 + 2,600 + 18,000) ÷ 360 ≈ 83.89%.
Why is the weighted average different from the simple average?
Because the groups are different sizes. The simple average counts each percentage once, so 40 students at 65% weigh as much as 200 at 90%. Weighted by size, the large class counts five times as much as the small one, which moves the average from 78.33% to 83.89%. With equal sizes the two are the same.
Is the average percentage the same as the overall percentage?
Not in general: the average that equals it is the weighted one. The overall percentage pools the counts: if classes of 120, 40 and 200 students pass at 80%, 65% and 90%, then 302 of 360 students passed, which is 83.89%, and that equals the weighted average. The simple average, 78.33%, equals it when every group is the same size (or every percentage is the same), and here it does not.
What is the average of two percentages?
Half their sum, if the two groups are the same size: 40% and 60% average 50.00%. If 100 people are at 40% and 300 at 60%, the average is (4,000 + 18,000) ÷ 400 = 55.00%.
How do you average percentages with different sample sizes?
Multiply each percentage by its sample size, add the products, and divide by the total sample size. It is the same as pooling the samples: 80% of 120, 65% of 40 and 90% of 200 are 96 + 26 + 180 = 302 out of 360, which is 83.89%.
Do the sample sizes have to add up to 100?
No. Only their proportions matter: 120, 40 and 200 give 83.89%, and so do 12, 4 and 20 (83.89%). Shares such as 30% and 70% work too: type them all with a % sign or all without.
How do I average percentages in Excel?
For a simple average use =AVERAGE(A2:A4). For a weighted one, put the sizes in column B and use =SUMPRODUCT(A2:A4,B2:B4)/SUM(B2:B4). If the cells are formatted as percentages, Excel stores 80% as 0.8 and the result comes back as a fraction, which the same formatting shows as a percentage. The same formulas work in Google Sheets.
Can an average percentage be over 100%?
Only if some of the percentages are. Growth figures of 120%, 135% and 90% average 115.00%. An average always lies between the smallest and the largest percentage, so it can pass 100% only when at least one input does.
When is averaging percentages wrong?
When the groups differ in size and you want the overall rate: weight by size instead. When the percentages are marks out of different totals: 80% of 50 and 60% of 100 are 66.67% overall, not 70.00%. And when they are changes over time: +10% and then −10% leave 99% of the start, because each change applies to a different base. That is compounding, not an average, which is why this calculator takes no negative percentages.