Changing Size of Legend in Altair

As you have seen, the legend has a default size in pixels that is constant regardless of the size of the chart. If you would like to adjust it, you can use the configure_legend() chart method.

In Altair 3.0 or later, the following arguments are the relevant ones for adjusting the size of the legend gradient:

chart.configure_legend(
    gradientLength=400,
    gradientThickness=30
)