You can use custom fonts in your Flutter application by including them in your flutter.yaml file under the fonts heading:

  - family: Raleway
      - asset: assets/fonts/Raleway-Regular.ttf
      - asset: assets/fonts/Raleway-Medium.ttf
        weight: 500
      - asset: assets/fonts/Raleway-SemiBold.ttf
        weight: 600
  - family: AbrilFatface
      - asset: assets/fonts/abrilfatface/AbrilFatface-Regular.ttf

The family determines the name of the font, which you can use in the fontFamily property of a TextStyle object to use the font with a Text or a RichText widget.

The asset is a path to the font file, relative to the flutter.yaml file. These files contain the outlines for the glyphs in the font. When building your app, these files are included in your app’s asset bundle.

A single font can reference many different files with different outline weights and styles:

  • The weight property specifies the weight of the outlines in the file as an integer multiple of 100 between 100 and 900. These values correspond to the FontWeight and can be used in the fontWeight property of a TextStyle object.

  • The style property specfies whether the outlines in the file are italic or normal. These values correspond to the FontStyle and can be used in the fontStyle property of a TextStyle object.

If a TextStyle object specifies a weight or style for which is there is no exact font file, the engine uses one of the more generic files for the font and attempts to extrapolate outlines for the requested weight and style.