The read-only fontBoundingBoxDescent property of the TextMetrics interface returns the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline attribute to the bottom of the bounding rectangle of all the fonts used to render the text, in CSS pixels.

A number, in CSS pixels.

The code below shows how you can get the fontBoundingBoxDescent for text in a particular font.

const canvas = document.createElement("canvas");
const ctx = canvas.getContext("2d");

ctx.font = "25px serif";
const text = "Foo";

const textMetrics = ctx.measureText("foo"); // returns TextMetrics object
const descentCssPixels = textMetrics.fontBoundingBoxDescent;

The descent in CSS pixels for the text "Foo" in a 25px serif font is shown below.

• TextMetrics.fontBoundingBoxAscent
• TextMetrics