What is a histogram?
A histogram splits a range of numbers into equal intervals, called bins, and draws a bar for how many values fall into each bin. Unlike a bar graph, the bars touch, because the bins are next to each other on one continuous scale.
A histogram answers questions a single average can’t: are most values close to the middle? Is the data lopsided? Are there two groups? Are there values far from the rest?
How to read a histogram
- Centre: where the tallest bars are. Compare it with the mean and median shown under the chart.
- Spread: a wide histogram means values vary a lot; the standard deviation puts a number on it.
- Shape: a long tail to the right (skewed right) is common for prices, incomes and waiting times; there the median is a better “typical value” than the mean.
- Two peaks: often means two different groups are mixed, such as weekday and weekend orders.
- Isolated bars: values far from the rest are worth checking. A box plot marks them as outliers.
How many bins should a histogram have?
There is no single right number. Common rules of thumb are the square root of the number of values, or Sturges’ rule (about 1 + log₂ n). With 100 values, both suggest roughly 8–10 bins. SheetGlance starts from a suggestion like this, and you can change it from 3 to 30.
Too few bins hide the shape; too many make the chart look like noise. Try a few settings: if the overall shape stays the same, you can trust it.
How to make a histogram in Excel
- Select the column of numbers.
- In Excel 2016 or later, go to Insert → Charts → Insert Statistic Chart → Histogram.
- Right-click the horizontal axis and choose Format Axis to set the Bin width or Number of bins.
In older versions, enable the Analysis ToolPak and use Data → Data Analysis → Histogram, which needs a separate column of bin limits. Excel doesn’t list the mean, median and quartiles next to the chart; SheetGlance shows them automatically.
How to make a histogram in Google Sheets
- Select the column and choose Insert → Chart.
- Under Setup → Chart type, choose Histogram chart.
- Under Customise → Histogram, set the Bucket size to control the bin width.
Histogram or bar graph?
Use a histogram for one numeric variable, such as test scores or delivery times, where the bins are ranges on a number line. Use a bar graph for separate categories, such as subjects or stores, where each bar is its own thing and the order can change.