How to Make a Histogram Online (With Bell Curve)

To make a histogram, open the Histogram Maker and paste your numbers — a column copied from a spreadsheet, or values separated by commas, spaces or new lines. The histogram appears straight away with Automatic bins. Switch to a set Number of bins or a fixed bin Width, turn on the bell curve to compare with a normal distribution, and download a PNG, JPG or SVG.

Make a histogram step by step

1. Open the Histogram Maker.
2. Paste or type your numbers in the Data box — test scores, heights, delivery times, prices.
3. Under Bins, choose:
   • Automatic — a sensible bin width (the Freedman–Diaconis rule), rounded so bins start on round numbers.
   • Number — split the range into that many equal bins.
   • Width — set the bin width and where the first bin starts (for example, width 10 starting at 50).
4. Under the options, tick Normal (bell) curve to compare the shape with a normal distribution, Show percentages instead of counts, and Values on bars.
5. Set the title and labels, then download PNG, SVG or JPG.

Reading a histogram

A histogram shows how values are spread: each bar counts how many values fall in a range (a bin).

• Centre — where the tallest bars are.
• Spread — how wide the bars stretch.
• Shape — symmetric (bell-shaped), skewed right (a long tail of high values, like incomes), skewed left, or with two peaks (two groups mixed together).
• Outliers — isolated bars far from the rest.

Histogram vs bar chart

They look alike but answer different questions:

• A histogram groups one continuous measurement into ranges; bars touch because the ranges are continuous.
• A bar chart compares separate categories (regions, products); bars have gaps and can be reordered.

Choosing bins

Bin choice changes the story:

• Too few bins hide the shape — everything looks like one lump.
• Too many bins make noise — gaps and spikes that mean nothing.
• Round widths (5, 10, 25) make the axis readable: "60–70" beats "61.3–68.9".

Start with Automatic, then try a round width close to it.

How edges are counted

Each bin includes its left edge and excludes its right edge — a score of exactly 70 goes in the 70–80 bin, not 60–70 — except the last bin, which includes both ends so the maximum is counted.

The bell curve

The normal curve uses your data's mean and standard deviation. If the bars follow it closely, the data is roughly normal — useful before running tests that assume normality. Big differences (skew, two peaks) are worth investigating.

A worked example: test scores

Paste a class's 60 test scores and choose Width 10 starting at 0. Bars for 50–60, 60–70, 70–80 and so on show at once where most students landed. A long tail on the left means a few students struggled; two separate peaks might mean two groups — perhaps two classes taught differently — worth looking at separately in a box plot.

Related charts

• Compare the spread of several groups: the Box Plot Maker.
• Relationship between two measurements: the Scatter Plot Maker.

Privacy

Your numbers stay in your browser — nothing is uploaded or stored.

Frequently asked questions

How many numbers do I need?

At least 20–30 for a meaningful shape; a few hundred or more is better.

Can I paste numbers with commas as thousands separators?

Put one number per line when values contain commas, so they aren't split.

Can I show percentages instead of counts?

Yes — tick Show percentages instead of counts, and each bar shows its share of all the values.