To find the average (arithmetic mean), add all the numbers and divide by how many there are. For 10, 20, 30 and 40 the sum is 100 and the count is 4, so the average is 25. Paste numbers separated by commas or spaces and the calculator returns the mean. Definition source: NIST/SEMATECH e-Handbook, Measures of Location.
It is the everyday mean for grades, simple stats warmups, and quick checks before deeper statistics work. For letter grades weighted by credit hours, use the GPA calculator. For percent comparisons against a target, use the percentage calculator. Round a long mean to the nearest tenth or hundredth with the rounding calculator.
How the formula works
average = sum / count. Every listed number contributes equally. There is no weighting and no dropping of high or low values unless you remove them from the list yourself.
Worked example
10 + 20 + 30 + 40 = 100. Count = 4. Average = 100 / 4 = 25.
| Input | Value |
|---|---|
| Values | 10, 20, 30, 40 |
| Sum | 100 |
| Count | 4 |
| Average | 25 |
Average examples
| Numbers | Sum | Count | Average |
|---|---|---|---|
| 10, 20, 30, 40 | 100 | 4 | 25 |
| 88, 92, 79, 85 | 344 | 4 | 86 |
| −5, 0, 5, 10 | 10 | 4 | 2.5 |
| 10, 20, 30, 400 | 460 | 4 | 115 (median 25) |
Quiz scores such as 88, 92, 79 and 85 average to 86. Always state how many scores entered the mean. To turn an averaged score into a letter grade, use the grade calculator.
Weighted average
- Formula: weighted average = Σ(value × weight) ÷ Σ(weights).
- Example: scores 80, 90 and 70 weighted 30%, 30% and 40% give (24 + 27 + 28) ÷ 1 = 79. The unweighted mean is 80.
- Group example: 20 students averaging 70 and 30 averaging 80 give (1,400 + 2,400) ÷ 50 = 76, not 75.
This calculator is unweighted. For a weighted result, list each value as many times as its weight, or use the formula above.
Mean vs median vs mode
The mean adds every value and divides by the count, so one extreme number moves it. The median is the middle value after sorting and the mode is the most common value.
For median, mode and range together, use the mean, median, mode and range calculator.
How to use the fields
- Enter each number in the list field as the tool allows.
- Confirm the count matches how many values you meant to include.
- Read the mean as sum divided by that count.
Equal weight assumption
Each value pulls the mean with the same strength. If one exam should count double, this unweighted average is the wrong model until you expand or weight the data.
Common mistakes
- Dividing by the wrong count after deleting a value
- Inserting zeros for missing data that should be omitted
- Confusing average with median or mode
- Averaging percentages that came from different sample sizes without care
Outliers
One extreme value can swing the mean. Report the mean with a note about outliers, or show a second mean after a documented exclusion so readers see both.
Rounding
Decide how many decimals your audience needs. Keep full precision in the sum step, then round the final mean once.
If you average rounded inputs, say so, because early rounding can bias the result slightly.
When mean is a poor summary
Skewed income style data or tiny samples can make a lone mean misleading. Pair it with count, and consider median in those stories even if this tool stays on the arithmetic mean.
Data entry hygiene
Comma separated lists fail when a decimal uses a comma in some locales. Keep a consistent decimal point style in the tool. Recheck count after paste operations that may insert blank tokens.
If a value is missing, omit it rather than typing zero, unless zero is a measured result. False zeros drag the mean downward without representing real observations.
Reporting the mean clearly
Write average, count, and the list summary together: mean 25 from four values 10, 20, 30, 40. That sentence is audit friendly. A bare 25 without context invites wrong comparisons.
Limitations
Unweighted arithmetic mean only. No automatic outlier filter, no weighted mean mode, and no full descriptive statistics suite on this page.