How to write a figure legend [Manuscripts and scientific papers]

Writing a compelling scientific manuscript requires clarity in both the main text and accompanying figures. An often underappreciated but crucial element of a successful paper is the figure legend, or caption, which provides an explanatory narrative for each visual display of data, such as a chart, graph, or schematic.

Figure and table legends are not simply descriptive but should be a blend of description and key results, helping the reader understand what the figure or table is showing without having to refer back to the main text.

The titles and legends for your figures and tables should be able to stand alone, enabling the reader to grasp the essence of the data without reading the main text.

Here’s everything you need to know about creating an awesome figure legend.

What is a figure legend?

A figure legend is a descriptive and explanatory piece of text that accompanies a figure in a manuscript, such as a graph, schematic, or chart.

Serving as a caption, it is integral to the understanding of the figure without needing to read the main text.

The format of a legend often includes a title in a declarative form summarizing the result or content of the figure, followed by details about the figure elements. For instance, it explains what various colors, symbols, or abbreviations used in the figure represent.

It should mention specific components, like error bars, which show the variability of data, p-value indicating statistical significance, and scale bars specifying actual dimensions in images.

It may also highlight the sample size used in an experiment. 

Legends typically present information in the past tense, as they describe completed work.

While figures visually present findings in the results section, figure legends offer the narrative linking the figure to the method section and provide the necessary context.

A well-written figure legend is crucial for effective communication in scientific publications.

What to include in your figure legend – features of a good figure legend

A good figure legend is both comprehensive and concise, giving the reader all necessary information to understand the figure without needing to refer back to the main text. The legend can either explain the experiment conducted or describe the result obtained, but whichever approach is chosen, consistency throughout the document is key.

Key PointsDescriptionExamples
ContentExplain the experiment or describe the result“Western Blot for protein depletion” (experiment) or “IQ gap is significantly depleted after knockdown” (result)
ConsistencyKeep a consistent approach throughout the documentIf you choose to explain the experiment in the first figure legend, continue with the same approach in subsequent legends
DetailDescribe all components of the figure“Figure 1A shows the control group in red. The asterisk indicates a significant difference, with a p-value of <0.05”
Alignment and LabelingAlign multiple images or graphs properly and label them correspondinglyFigure 1A (bar chart), Figure 1B (line graph), Figure 1C (scatter plot)
FormattingUse a consistent font type and size, labels, and color schemeArial font, size 12, control group consistently in red
LegibilityMake sure all text and data points are easily readableAvoid cluttered graphs, ensure text is large enough to read comfortably
Statistical ComparisonsShow significant statistical comparisons“The asterisk between the first and third bars signifies a significant difference”
Color and Symbol ExplanationExplain the meaning of different colors and symbols used“In Figure 1A, red represents the control group while blue represents the treatment group. The arrow indicates the trend.”

All components of the figure, such as different parts labeled A, B, C etc., must be clearly described.

This should include explanations of all symbols, colors, or arrows used, along with specific values such as p-values for statistical significance, the scale bar size, etc. Any statistical comparisons, such as an asterisk showing a significant difference between two bars, should also be noted.

If multiple images or graphs are present, they should be aligned properly and labeled correspondingly, e.g. figure 1A, 1B, etc.

This helps to direct the reader to the appropriate image when discussing it in the text.

Keep the formatting consistent with the font type and size, labels, and color scheme across all figures in your document.

Attention to these details not only enhances readability but also gives a professional and polished appearance to your work.

Examples of Well-Written Figure Legends

My top tips for how to write a figure legend

  • Be Descriptive: Clearly explain what the figure is about and what it represents.
  • Include a Title: Give your figure a concise, informative title that summarizes its key point or result.
  • Refer to the Figure Directly: Use ‘Figure 1 shows…’ instead of ‘the following figure shows…’.
  • Keep it Concise: While being descriptive, keep the caption brief and to the point.
  • Use Past Tense: You are describing work that has been completed.
  • Define All Symbols and Abbreviations: Do not assume the reader knows what certain symbols or abbreviations mean.
  • Specify Sample Size: If applicable, provide the number of observations.
  • Explain Error Bars: If error bars are included in the figure, explain what they represent.
  • Indicate Scale Bars: For images, include scale bars and explain their size.
  • Mention p-values: If statistical testing was used, provide the value to show if the result was significant.
  • Use Consistent Formatting: Follow a consistent format for all the figure legends in your document.
  • Avoid Repetition: Do not repeat information that’s already in the main text or in the methods section.
  • Label Parts of the Figure: If your figure has multiple parts, label them as ‘A’, ‘B’, etc., and explain each part in the legend.
  • Consider Figure Legends as Standalone Texts: A reader should understand the figure without referring to the main text.
  • Use Proper Grammar and Spelling: As with the rest of your manuscript, legends should be well-written.
  • Explain Color Coding: If you use colors in your figure, explain what each color indicates.
  • Clarify the Main Findings: Summarize what the figure is demonstrating in relation to your study.
  • Point Out Important Features: Direct the reader to important elements or findings in the figure.
  • Stay within the Journal’s Word Limit: Many journals limit the length of figure legends, so ensure you comply.
  • Ask for Feedback: Have a colleague or mentor read your figure legend to make sure it’s clear and understandable.

Wrapping up – Good figure legends

A well-crafted figure legend, like the lyrics to a melody, provides context, meaning, and understanding to the visual data represented in a scientific manuscript.

Not merely descriptive, the figure legend or caption serves as an insightful guide that ensures the reader can comprehend the figure without having to refer back to the main text. Indeed, the success of your research paper largely hinges on the effectiveness of your figure and table legends.

Crafting an effective figure legend is as much an art as it is a science.

It is a finely tuned balance between providing enough detail without overwhelming the reader.

This balance ensures that the figure is showing exactly what you intend and that the reader can understand what the figure depicts.

The information to include ranges from the type of analysis conducted to the numbers of replicates used in the study.

Each component of the figure, from ‘Figure 1A’ to ‘Supplementary Figure 1’, requires its own concise, yet comprehensive, explanation.

A table or figure is used to convey complex research data, and its corresponding legend acts as the explanatory text, unraveling the intricacies of your findings.

Whether it’s Table 1A, Table 1B, Figure S1, or Supplementary Table 1, each needs its own descriptive figure legend.

Furthermore, as part of your research writing, it’s key to observe your target journal’s guidelines for caption writing, including any word limit restrictions for your figure legends. 

Your ability to write figure and table legends in a concise, understandable, and effective way not only enhances the quality of your published papers but also reinforces your credibility as a researcher.

So, as you embark on the journey of writing an effective figure legend for your next scientific paper, bear in mind these tips for writing. By doing so, you’ll ensure your figure legends are not merely descriptive but also insightful and illuminating.

They should enrich your manuscript and illuminate the path for your reader to better understand your research findings.

The Author

Dr Andrew Stapleton has a Masters and PhD in Chemistry from the UK and Australia. He has many years of research experience and has worked as a Postdoctoral Fellow and Associate at a number of Universities. Although having secured funding for his own research, he left academia to help others with his YouTube channel all about the inner workings of academia and how to make it work for you.