Adjust UIButton font size to width

Try this:

button.titleLabel?.numberOfLines = 1
button.titleLabel?.adjustsFontSizeToFitWidth = true
button.titleLabel?.lineBreakMode = .byClipping //<-- MAGIC LINE

I'm not sure why this does the trick but it does :)

button.titleLabel.adjustsFontSizeToFitWidth = YES;

should do the work on its own if you are using Auto-Layout and have set a constraint on the button's width.

The other options (minimum scale factor, number of lines etc) can still be used to customize further according to your needs, but are not required.