Histogram Maker

Paste numbers from a spreadsheet and turn them into a clear histogram.

Control the bin count, width, and starting value, add a fitted normal curve, then export PNG or SVG or print in black and white.

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How raw numbers become a histogram

Imagine 24 quiz scores spread from 51 to 96. A list preserves every score, but it hides the shape. A histogram replaces that list with equal-width intervals and counts how many scores land in each one. Five students in the 70-to-under-80 interval become one bar with a height of five. The bars touch because the intervals form one continuous number line rather than separate categories.

The boundary rule is the part that prevents double counting. This tool uses lower-inclusive, upper-exclusive intervals: 70 ≤ x < 80 includes 70 but not 80. A score of exactly 80 enters the interval beginning at 80. Only the final interval includes its upper end, which guarantees that the maximum is not lost. The green integrity message checks the result after every edit and confirms that the sum of all bin frequencies equals the number of valid values.

Labels remain attached to rows in the editor so you can find and correct a student or measurement. They do not become categories on the chart. That distinction matters: a histogram shows the distribution of numeric values, while a bar graph compares named groups.

Choosing a bin count, width, and starting value

The same values can look smooth, lumpy, or almost flat depending on the bins. Automatic mode starts with Sturges' rule, ceil(log2(n) + 1). A set of 16 values gets 5 bins; 32 values gets 6; 64 values gets 7. That slow growth keeps a small dataset from being split into dozens of nearly empty bars.

  • Choose a bin count when the class needs a fixed number of groups. The width is calculated from your starting value through the maximum.
  • Choose a bin width when the interval itself has classroom meaning, such as 10-point score bands, 5 cm height bands, or 30-second time bands.
  • Choose the starting value to put boundaries on useful numbers. Starting score bins at 50 with a width of 10 produces 50–under 60, 60–under 70, and so on.

A starting value cannot sit above the minimum because that would leave observations out. The tool stops and explains the problem instead of hiding those values. If a narrow manual width would produce more than 80 bars, it also asks for a wider interval so labels and printed lines stay readable.

Reading shape, center, spread, and the normal curve

Read the chart and the six-number summary together. The median marks the middle observation after sorting. The mean uses every value, so one unusually high or low result can pull it away from the median. Population standard deviation measures spread around the mean using every value shown; a larger number means the values are more dispersed in the same units as the horizontal axis.

The optional normal curve is calculated from that mean and standard deviation. Its probability density is multiplied by the number of observations and the bin width, turning it into expected frequency on the same vertical scale as the bars. The curve uses a dashed line while the data uses solid outlined rectangles, so the two remain distinct without relying on color.

Treat the overlay as a comparison, not a verdict. With 12 scores, a roughly bell-shaped pattern can happen by chance. Skew, gaps, clusters, and possible outliers may change when you alter the bins. Compare at least two reasonable settings before making a claim about the distribution, and keep the raw values when individual decisions depend on them.

A quick classroom workflow from spreadsheet to worksheet

Copy the Label and Value columns from a spreadsheet and paste them into the blue box. The tool recognizes tab-separated spreadsheet cells, comma-separated text, and one value per line. Check the status chips before reading the chart: numeric rows are included, empty rows are ignored, and rows that need attention are named so you can correct the source rather than hunting through every cell.

  1. Start with automatic bins and press Use lowest value if the current start excludes a new minimum.
  2. Add a specific title and units on the horizontal axis. Use frequency, students, trials, or another honest count on the vertical axis.
  3. Open Exact bin counts and check both the interval notation and the total before sharing the chart.
  4. Download SVG for a worksheet or slide, PNG for a quick image, or print a black-on-white landscape page. Letter and A4 are sized separately.

Long titles and axis labels wrap, crowded boundary labels rotate, and charts with many bins show a smaller set of axis ticks without removing any bars. All work stays inside the browser, including exported files, so student labels and scores are not sent to a server.

Frequently Asked Questions

Common questions about the Histogram Maker

Automatic mode uses Sturges' rule: ceil(log2(n) + 1), where n is the number of valid values. For 32 values, log2(32) is 5, so the tool makes 6 equal-width bins. It is a dependable starting point for small and medium classroom datasets, and you can still switch to a manual count or width.
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Sources & References

Statistical methods and formulas

Definitions and worked methods for descriptive and inferential statistics.
→Source: NIST/SEMATECH e-Handbook of Statistical Methods

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