Font metric overrides | Frontend Practical Guide

Browser support

Feature	Desktop				Mobile
Feature	Chrome	Edge	Firefox	Safari	Chrome Android	Safari iOS
`api.FontFace.ascentOverride`	87	87	89		87
DOM API
`descentOverride` The descentOverride property of the FontFace interface returns and sets the value of the @font-face/descent-override descriptor. The possible values are normal, indicating that the metric used should be obtained from the font file, or a percentage.	87	87	89		87
`lineGapOverride` The lineGapOverride property of the FontFace interface returns and sets the value of the @font-face/line-gap-override descriptor. The possible values are normal, indicating that the metric used should be obtained from the font file, or a percentage.	87	87	89		87
CSS at-rule
`ascent-override` The ascent-override CSS descriptor for the @font-face at-rule defines the ascent metric for the font. The ascent metric is the height above the baseline that CSS uses to lay out line boxes in an inline formatting context.	87	87	89		87
`descent-override` The descent-override CSS descriptor for the @font-face at-rule defines the descent metric for the font. The descent metric is the height below the baseline that CSS uses to lay out line boxes in an inline formatting context.	87	87	89		87
`line-gap-override` The line-gap-override CSS descriptor for the @font-face at-rule defines the line-gap metric for the font. The line-gap metric is the font recommended line-gap or external leading.	87	87	89		87

1+Supported (version) Not supported ※Has note Sub-feature descriptions sourced from MDN Web Docs (CC BY-SA 2.5)

CSS

@font-face {
  font-family: "Adjusted Fallback";
  src: local("Arial");
  ascent-override: 90%;
  descent-override: 22%;
  line-gap-override: 0%;
}

CSS o-ba-raid with demo.

CSS Normalfont demo.

CSS comparison view demo.

Refine text rhythm

Use Font metric overrides to make long-form reading or dense interface copy easier to scan and understand.
Support language nuances

Apply Font metric overrides when different writing systems or typographic conventions need more deliberate control.

Test Font metric overrides in the browsers you support, especially if it changes layout, text handling, or interaction behavior.
Plan a fallback or acceptable degradation path when support is still limited.