How to Write Figure Legends

A figure legend (caption) explains what a figure shows so that it can be understood without reading the text. It should state what is plotted, in whom, how data were summarised and what symbols mean.

What to include

1. A title sentence stating the main point or content.
2. What is shown: variables, groups, time points, sample sizes.
3. Symbols, lines, colours and abbreviations.
4. Statistical information: summary measure (mean, median), error bars (SD, SE, 95% CI), tests, and n.
5. Source and permissions if adapted from elsewhere.
6. Scale or magnification for images, and arrows or panel letters.

Writing tips

• Keep it concise, but complete enough to stand alone.
• Define each abbreviation in the legend, even if defined in the text.
• State what error bars represent, because journals often require this.
• Avoid describing the conclusion at length; the text handles that.

Illustrative example

Invented for teaching. Weak: "Figure 2. Blood pressure results." Strong: "Figure 2. Change in systolic blood pressure from baseline to 12 weeks in the exercise (n = 60) and usual care (n = 60) groups. Points are individual changes; horizontal bars show means with 95% confidence intervals. Mean difference −5 mm Hg (95% CI −9 to −1; independent t-test)." (Invented data.)

Reuse and permissions

If you reproduce or adapt a published figure, you need permission and an acknowledgement. Open-licence figures still require attribution according to the licence.

Legends for different figure types

For a flow diagram, state the study and what each box represents. For a Kaplan–Meier curve, give the groups, the number at risk, the time unit and any test used. For a forest plot, say what the squares, lines and diamond represent and the model used. For a clinical image, state the view or stain, the scale and what the arrow points to, and confirm that consent covers the image.

Common pitfalls

• Not stating whether error bars are SD, SE or CI.
• Legends that depend on the text to be understood.

Key takeaways

• A legend should let the figure stand alone.
• State n, summary statistics and the meaning of error bars.

This page is general educational information about research methods. It is not medical, legal or regulatory advice; follow your institution's ethics board and your target journal's instructions.