Introduction
Figure legends are a key element of scientific writing, whether for a journal paper, dissertation or PhD thesis. A well written figure legend can make all the difference between a legend that conveys useful information about your methods or results and one that is almost incomprehensible.
The specific formatting requirements of a figure legend will vary depending on the context and document type. However, there are several basic commonalties to be aware of with caption writing.
You write a figure legend so that the reader can fully understand the content of your figure without having to refer to the main text. Figure legends are written alongside the actual figures, separately from the main text and should be concise and to the point.
How to write a Figure Legend
Consider the following elements when writing your figure legend:
The Title
The figure title should be a short title that is applicable to the entirety of the content of the figure. You may use it to describe what the figure is showing or use it to state a key point such as an important result. If presenting a results graph, then you can start the title sentence as “pie chart showing….” or “scatter plot of…” etc.
The Methods
If your figure is showing an experimental setup, perhaps as a schematic overview, then it should be detailed enough to explain what the materials and methods shown were. Remember that a reader should be able to glean the key information from the figure legend without reading the main methods text.
It can be tempting to add too much information but keep it to the essential details only. Be aware that some journals may insist that this level of detail is kept to the main body of text (i.e. the methods section) rather than the figure legends themselves.
The Results
This of course is only relevant if you’re presenting a result in your figure. It’s common here that the main title heading of your figure legend will provide enough detail about the key result. You therefore may not need to write anything extra other than clarifying the level of statistical significance if appropriate.
Avoid any repetition with what’s already in the results section and double check the university or journals specific requirements for legend formatting.
The Definitions
Explain any feature in your figure that may be ambiguous. For instance, spell out any acronyms used, describe the significance of different colours or patterns on your bar graph and clarify what the lines on your box plot represent.
Clarify what the scale bars and error bars mean if you think there may be any confusion about these.
Other Important Points
They key with writing an effective figure legend is that you don’t use anymore words than you need to. Stay consistent with the tense used in sentences and keep the writing style aligned with that of the main body of text.
Write in the past tense when describing the methodology that was used. Stay in the present tense when explaining a result or definition.
Use a numerical digit as the figure number rather than the full word, e.g. Figure 1. rather than Figure One.
The font size for the figure legend is normally one size smaller than that of the main text (e.g. size 12 vs size 11).
If in doubt about how to format your figure caption, a safe option is to use the APA style.
When preparing a manuscript for publication, some journals will ask you to include each legend entry just before or after your reference list (rather than within the main text). When writing a table legend, these may be asked to be within the main manuscript or some journals ask each table and corresponding table legend to be within a separate Microsoft Word document during the initial submission. It’ll be your responsibility as the corresponding author to make sure you understand the requirements before submitting your manuscript.
Overall, keep it simple. Use plain English where you can any write everything as a complete sentence.
Examples of Well Written Figure Legends
When you read a scientific paper published in one journal to the next, you’ll notice the differences in the way the figure legend is written. For example some may be very short (one sentence), whilst others will read more like a long paragraph. These variations may also exist with the same journal and be dependent on the article type.
We’ve collected a range of examples of open-access journal papers that have written effective figure legends.
Check them out by clicking on the article titles below:
