Definitions
- Mean (average): add all the values and divide by how many there are.
- Median: the middle value once the data is sorted. For an even count, the average of the two middle values.
- Mode: the value that appears most often. There can be none, one or several.
- Range: largest value minus smallest value.
Worked example
Data: 3, 7, 7, 2, 9, 4, 7.
- Mean: 3 + 7 + 7 + 2 + 9 + 4 + 7 = 39, and 39 ÷ 7 ≈ 5.571.
- Median: sorted, the list is 2, 3, 4, 7, 7, 7, 9. The 4th of 7 values is 7.
- Mode: 7 appears three times, more than any other value.
- Range: 9 − 2 = 7.
Mean vs. median: which to report?
When the data is symmetric, the mean and median are close, and either is fine. When the data is skewed, they split apart: a few very high incomes raise the mean income far above what a typical person earns, while the median stays put. As a rule, report the median for skewed data and the mean for symmetric data. A histogram shows which you have.
Have grouped data (a frequency table) instead of raw numbers? Use the grouped data calculator.
Why the mean, median and mode can disagree
Take incomes (in $1,000s) for 10 people: 32, 35, 38, 41, 45, 48, 52, 58, 64 and 250. The mean is 66.3, but nine of the ten people earn less than that. The median, 46.5, is a far better description of a typical income here. One very high value is enough to pull the mean away from everyone else.
Which average should you use?
| Your data | Best average | Why |
|---|---|---|
| Roughly symmetric numbers (heights, test scores) | Mean | Uses every value; close to the median anyway |
| Skewed numbers or outliers (incomes, house prices, wait times) | Median | Not pulled by extreme values |
| Categories (favorite color, shoe brand) | Mode | The only average that works for non-numbers |
| Discrete counts (children per family) | Median or mode | “2.3 children” isn’t a real family |
Weighted mean
When values count unequally, multiply each by its weight, add, and divide by the total weight. A course with homework worth 20% (score 90), a midterm worth 30% (score 75) and a final worth 50% (score 82) gives (0.2 × 90 + 0.3 × 75 + 0.5 × 82) ÷ 1 = 81.5, not the simple average of 82.3.
Common mistakes to avoid
- Finding the median without sorting. The median is the middle of the sorted list, not of the list as typed.
- Forgetting to average the two middle values. With an even count, the median is the average of the two middle values.
- Saying “no mode” when there are two. If two values tie for most frequent, both are modes (the data is bimodal).
- Reporting only the mean for skewed data. Give the median too, or readers will picture the wrong typical value.
Mean, median and mode in Excel, Google Sheets, TI-84 and Python
| Software | How |
|---|---|
| Excel | =AVERAGE(range), =MEDIAN(range), =MODE.SNGL(range); =MODE.MULT(range) lists every mode. |
| Google Sheets | =AVERAGE, =MEDIAN and =MODE (or MODE.MULT). |
| TI-84 | STAT › CALC › 1-Var Stats gives x̄ (mean) and Med; there is no built-in mode. |
| Python | statistics.mean, statistics.median and statistics.multimode(data). |
Related tools: Standard Deviation Calculator, Five-Number Summary Calculator, Grouped Data Calculator, Dot Plot Maker and Descriptive Statistics Calculator.