Examples
Worked examples
- Is an instance
A figure legend for a bar-chart figure reads: 'Figure 3. Cell viability decreased with increasing drug concentration. (A) Viability at 24 hours across five concentrations (n = 6 independent experiments per group). (B) Viability at 48 hours, same conditions. Error bars represent standard deviation; statistical significance was assessed by one-way ANOVA with Tukey's post hoc test (*p < 0.05, **p < 0.01). Scale bar in inset micrograph = 50 micrometers.' A reader can determine what was measured, how many replicates were run, and which statistical test produced the significance markers without consulting the Methods section.
- Is an instance
A micrograph figure's legend defines every abbreviation used on the image itself -- for example, spelling out 'DAPI (4',6-diamidino-2-phenylindole, nuclear stain)' and 'GFP (green fluorescent protein)' the first time those labels appear in the figure, even if the same abbreviations were already defined earlier in the manuscript text, because a reader may view the figure without having read that earlier section first.
Counter-examples
Looks similar, but isn't
- Not an instance
The sentence 'Knockdown of the gene reduced expression significantly (Fig. 2C)' embedded in the Results section is an in-text figure reference, not a figure legend -- it is a pointer within the running narrative prose directing the reader to a specific panel, not the standalone caption text that accompanies the figure itself.
- Not an instance
A one-line caption reading only 'Figure 4. Western blot results.' with no panel description, no abbreviation definitions, no stated sample size, and no explanation of what the bands represent does not meet the standard for a complete figure legend -- it fails the standalone-comprehension test a legend is meant to satisfy.
Editorial commentary
A figure legend (also called a figure caption) is the explanatory text that accompanies a figure in a scientific manuscript — conventionally placed directly beneath the figure, or compiled together on a separate legends page or section, depending on the target journal’s submission format. Its defining function is standalone comprehension: a reader should be able to understand what a figure shows, and why it matters, from the figure plus its legend alone, without having to page back to the Methods or Results text to decode what a color, symbol, or abbreviation means.
What a complete figure legend includes
Because the legend has to carry that explanatory weight on its own, journals and style guides converge on a consistent set of required elements, even though exact word-count limits and formatting vary by publisher:
- A brief title sentence. A short, often declarative statement of the figure’s main point, result, or content — functioning as a one-line summary a reader can scan before reading the fuller description.
- A description of each panel. For multi-panel figures, the legend describes what each lettered panel (A, B, C…) shows, in the same order the panels are laid out in the image.
- Definitions of abbreviations, symbols, and codes. Any abbreviation, color code, line style, or symbol used in the figure itself — but not already defined in the immediately preceding text — needs to be spelled out in the legend, since a reader may encounter the figure (via a PDF, a slide, or a search-result thumbnail) before or without reading the surrounding prose.
- The statistical test and what error representations mean. If the figure shows error bars, shaded confidence bands, or significance markers, the legend states what they represent (standard deviation, standard error of the mean, a 95% confidence interval) and which statistical test produced any reported p-values.
- Sample size (n). The number of biological or technical replicates, participants, or observations underlying the figure, stated explicitly rather than left to be inferred from the Methods section.
- Scale information, where relevant. For micrographs, gels, or other images where size matters, a scale bar with its defined length.
Figure legends are conventionally written in the past tense, since they describe work that has already been completed, and are kept concise — many journals cap legend length explicitly (for example, Nature journals specify figure legends under 250 words; other publishers commonly allow up to around 300-350 words per legend). Authors should always confirm the exact word limit, placement convention, and formatting rules in the target journal’s own instructions for authors, since these details are set at the publisher or journal level and are not standardized industry-wide. See CASRAI’s Scientific Figure Rules for Journal Submission guide for the broader set of preparation requirements — resolution, file format, panel labeling, and image-integrity rules — that apply to the figure itself alongside its legend.
How a figure legend differs from an in-text figure reference
A figure legend is easy to conflate with an in-text figure reference (also called a figure callout) — a short pointer embedded in the manuscript’s running prose, such as ‘protein expression increased over the treatment period (Fig. 2A)’ or ‘as shown in Figure 3, the effect was dose-dependent.’ The two serve different, complementary purposes:
- An in-text reference lives inside the narrative flow of the Results or Discussion section. Its job is to direct the reader’s attention to a specific figure at the point in the argument where that evidence is relevant. It assumes the reader is following the manuscript’s prose in sequence and does not need to be self-explanatory on its own.
- A figure legend lives with the figure itself, physically separated from the narrative prose. Its job is to make the figure interpretable independent of that narrative — a reader who encounters the figure out of sequence (skimming a PDF, viewing a slide reproduction, or seeing the figure surfaced in a search result or a review) still needs to be able to understand it from the legend alone.
A manuscript needs both: in-text references that guide a linear reader through the argument, and legends that make each figure independently interpretable regardless of how or where it’s encountered.
Figure legend vs. a graphical abstract
A figure legend should not be confused with a graphical abstract. A graphical abstract is a single summary image, submitted as its own file, representing the paper’s central finding for search results, tables of contents, and social sharing — it is generally required to be understandable with little to no accompanying text and is not paired with a legend in the way an ordinary in-text figure is. A figure legend, by contrast, is the caption for one of the manuscript’s regular, numbered figures, and is expected to include substantially more explanatory detail (statistics, abbreviations, panel-by-panel description) precisely because it is doing the work the graphical abstract’s design deliberately avoids relying on text to do.
Why this matters for reproducibility and peer review
Beyond readability, complete figure legends are a practical reproducibility safeguard: a reviewer or reader assessing whether a figure’s statistics support its stated conclusion needs the test, the n, and what the error representation means stated directly in the legend, not left implicit or requiring a search through the Methods. Journals that enforce image-integrity policies (see CASRAI’s Scientific Figure Rules for Journal Submission guide for the related image-manipulation standards many journals apply) also rely on the legend to state clearly what manipulation, if any, has been applied and what each channel or overlay represents, which is part of why incomplete legends are a common cause of reviewer queries and revision requests.
References
- Nature, Springer Nature — figure preparation guidelines for initial and revised submissions.
- PLOS — figure requirements for journals.plos.org (captions required to appear in manuscript text, not embedded in the image file).
- Journal-specific instructions for authors (word limits, placement, and formatting vary by publisher).
Machine-readable encodings
Use in your systems
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