The core descriptive statistics
Given a set of numbers, a few measures summarise it. The mean is the average — the sum divided by how many there are. The median is the middle value when sorted, which resists being pulled by outliers. The mode is the most frequent value. Together they describe the centre of your data from three angles.
Spread: range, variance and standard deviation
The range is the gap between the smallest and largest values. Variance and standard deviation measure how far the numbers typically sit from the mean — a small standard deviation means the data is tightly clustered, a large one means it's spread out. This tool reports the sample standard deviation, which divides by n − 1 and is the usual choice for a sample of a larger population.
Sample vs. population
If your numbers are the entire group you care about, a population standard deviation (dividing by n) is technically correct; if they're a sample meant to represent something bigger, the sample version shown here is standard. For most everyday uses the difference is small, and it shrinks as your dataset grows.
Frequently asked questions
What if there's no repeated value?
Then there's no mode, and the tool says so. Mode only exists when at least one value appears more than once; there can also be several modes if values tie.
Mean or median — which should I use?
Use the mean for symmetric data, and the median when a few very large or very small values would distort the average, such as incomes or house prices.