How to resize a custom font using UIFontMetrics

Swift version: 5.10

Paul Hudson @twostraws May 28th 2019

Dynamic Type allows developers to adjust the size of in-app text based on user accessibility preferences, but if you use custom fonts it’s easy to forget to add support.

To combine custom fonts with Dynamic Type, you need to use UIFontMetrics. You create instances of this class by specifying what type of content you want to measure – e.g. headline text or body text – and once that’s done you can pass it a font and ask it to provide a scaled font back. This converts your custom font and size into a scaled font suitable for the user’s preferences.

Here’s an example in code:

if let font = UIFont(name: "Helvetica", size: 72) {
    let fontMetrics = UIFontMetrics(forTextStyle: .headline)
    label.font = fontMetrics.scaledFont(for: font)
}