I’ve been struggling to correctly size my ggplot2 or base plots in Quarto documents. The main problem I encounter is that when I change the width or size of a figure, the text in figures also changes in size, which makes the document look very inconsistent.

This post documents the (awesome) solution I stumbled upon and settled on. There is no explanation, just a series of steps. For discussion, see the links at the bottom of the post.

Step 1: Defaults

Set reasonable document-wide defaults:

knitr::opts_chunk$set(
    out.width = "70%", # enough room to breath
    fig.width = 6,     # reasonable size
    fig.asp = 0.618,   # golden ratio
    fig.align = "center" # mostly what I want
)

Step 2: Aspect ratio

For each figure, adjust the fig-asp code chunk as appropriate. For example:

```{r}
#| fig-asp: .7
plot(hp ~ mpg, data = mtcars)
```

fig-asp is a “free” parameter. You can adjust it as you please without a second thought.

Step 3: Width

Finally, set the width of your figure. This is a two step process:

Set out-width
Set fig-width based on the value of out-width

First, you decide what percentage of the horizontal space you want the figure to take. This is defined in terms of percentage by the out-width chunk option.

Second, use the out2fig() calculator to figure out what value of fig-width to select:

out2fig = function(out.width, out.width.default = 0.7, fig.width.default = 6) {
    fig.width.default * out.width / out.width.default 
}

For example, if you use the same defaults as me and want a figure to take up 95% of horizontal space in your document, set the fig-width chunk option to:

out2fig(0.95)

[1] 8.142857

```{r}
#| fig-asp: .7
#| out-width: 95%
#| fig-width: 8.142857
plot(hp ~ mpg, data = mtcars)
```

References

[https://r4ds.had.co.nz/graphics-for-communication.html#figure-sizing]
[https://www.tidyverse.org/blog/2020/08/taking-control-of-plot-scaling/]