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Box Plot Maker

Put data from several machines, lines or conditions side by side and compare their medians, interquartile ranges and outliers. Differences between groups are interpreted automatically.

1Data Table

Paste a table copied from Excel into a cell (Ctrl+V). Click a column header (A, B…) before pasting to use the first line as column names. Double-click a header to rename it, right-click to insert/delete rows and columns, and formulas such as =A1*2 work too.

2Box Plot Options

Select data columns to plot (multiple allowed):

※ When using a group column, select only one data column. The data are split by group value and drawn together on one chart.

Drawing mode for multiple selections
Box plot options

How to make a box plot

  1. Arrange the groups to compare in separate columns, or as one value column plus one group column.
  2. Copy the data and paste it into the data table (paste on a column header to use the first line as names).
  3. Select the columns to compare (or a value column and a group column).
  4. Press Draw and check box positions, outliers, statistics and the automatic interpretation.

What is a box plot?

A box plot summarizes a distribution with five numbers: the box spans the first quartile (Q1) to the third quartile (Q3), the line inside is the median, and the whiskers reach the most extreme values within 1.5 × IQR of the box. Points beyond the whiskers are drawn individually as outliers.

Because it is compact, it is ideal for comparing many groups at once - for example the same measurement from several machines, shifts or suppliers.

How quartiles and outliers are calculated

Quartiles use linear interpolation (the NumPy default), and the whiskers follow the standard matplotlib rule. The mean is marked with ◆ so you can see how far it sits from the median - a large gap suggests skewed data.

How to read a box plot

  • A taller box means more spread in the middle 50% of the data.
  • If the median line is not centered in the box, the distribution is skewed toward the longer side.
  • Outliers may be measurement errors or special causes - check what happened at those points.
  • Boxes that barely overlap suggest a real difference between groups; confirm it with a statistical test.

Frequently asked questions

Can I compare several groups on one chart?

Yes. Select several columns, or one value column with a group column, and each group gets its own box.

What counts as an outlier?

Values below Q1 − 1.5 × IQR or above Q3 + 1.5 × IQR, where IQR = Q3 − Q1. This is the same rule used by most statistical software.

Can I test whether the groups are significantly different?

The box plot shows the difference visually. ANOVA, t-tests and non-parametric tests are available in the Qstat desktop program.

Is my data sent to a server?

No. Everything is processed inside your browser and nothing is transmitted or stored.

Other chart tools

Histogram MakerSee the distribution, a fitted normal curve and Pp/Ppk against spec limits at once.Scatter Plot MakerPlot the relationship between two variables with a trendline, equation and R².Bar Chart MakerCompare values by category with vertical, horizontal, grouped or stacked bars.

Need process capability, control charts or DOE?

The Qstat desktop program offers about 250 analysis features: histograms and box plots plus process capability (Cp, Cpk), control charts, measurement system analysis (MSA), design of experiments (DOE), regression and machine learning.

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