Charts & Visualizations

Box Plot

A standardized way of displaying data distribution based on quartiles.

Definition

Box plots (also known as box-and-whisker plots) display the distribution of numerical data through quartiles. The box shows the interquartile range (IQR) with a line for the median, while whiskers extend to show the rest of the distribution, excluding outliers.

Examples

Distribution comparison between groups A and B

Chart Visualization

This example includes an interactive chart visualization with 2 data points.

Chart type: boxplot

Usage

Best Used For

  • Comparing distributions between groups
  • Identifying outliers
  • Showing data spread and skewness
  • Visualizing statistical summaries (median, quartiles)

Data Requirements

[Object]

When to use this chart

Creative test spread

Data shape: CPA distribution across ad variants (not just means)

Shows variance and outliers that bar charts of averages conceal

Source: Tukey (1977), exploratory data analysis; Wilke (2019)

Limitations

Important Considerations

  • ⚠Can hide underlying distribution shapes (e.g., bimodality)
  • ⚠May oversimplify complex distributions
  • ⚠Requires statistical literacy to interpret fully
  • ⚠Less intuitive for non-technical audiences than histograms

Best Used For

  • Comparing distributions between groups
  • Identifying outliers
  • Showing data spread and skewness
  • Visualizing statistical summaries (median, quartiles)

Supplemental Resources

Frequently asked questions

Common questions about Box Plot, answered.

What is a box plot?
A box plot (or box-and-whisker plot) summarizes a distribution using five numbers: the median (line in the box), the first and third quartiles (the box edges, spanning the middle 50% of values), and whiskers extending to the range of typical values, with points beyond drawn as outliers. It compresses a whole distribution into a compact shape, which is why it's the standard for comparing many groups side by side.
How do I read a box plot?
The line inside the box is the median (the typical value). The box spans the interquartile range (IQR) — the middle 50% of the data — so a tall box means high variability. Each whisker extends to the farthest data point that still falls within 1.5× the IQR of its quartile, so whiskers stop at actual data points rather than at a fixed distance, and any points beyond them are drawn individually as outliers. A median sitting off-center in the box, or one whisker much longer than the other, signals skew.
When should I use a box plot instead of a histogram?
Use a box plot when comparing the distributions of several groups at once — its compactness lets you line up many side by side and instantly compare medians, spread, and outliers. Use a histogram to understand the detailed shape of a single distribution, since a box plot can hide important features like bimodality (two peaks look the same as one in a box plot).
What do outliers in a box plot mean?
The dots beyond the whiskers are values that fall outside the expected range (typically more than 1.5× the IQR from the quartiles). They may be genuine extreme cases worth investigating, data-entry errors, or simply the natural tail of a skewed distribution. A box plot flags them for attention but doesn't judge them — always look at why they're there before excluding them.
What does a box plot hide?
Its strength — summarizing to five numbers — is also its blind spot: it can't show the shape within the box. Two very different distributions (one with a single peak, one with two) can produce identical box plots. When the detailed shape matters, overlay the raw points (a strip or jitter plot), use a violin plot, or pair the box plot with a histogram.

Related Terms

Histogram

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Density Plot

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Data Visualization

Mentioned in

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