Set a preferred reading size
Apple documents System Settings > Accessibility > Display > Text size. Move the slider for the supported apps, desktop text and sidebars. Individual listed apps can have a different size or their own customization.
Use a familiar paragraph and a sidebar label when comparing sizes. A larger value that helps a title may have a different effect on a dense list.
Compare display scaling and zoom
For a broader enlargement, Apple describes a Larger Text option in Displays settings. Accessibility > Zoom offers magnification of the screen or a region.
Preferred text size, display scaling and magnification are separate controls. Identify whether you need to enlarge only reading text or the entire interface.
Handle one affected application
If only one app is difficult to read, inspect its own view or text-size options before changing the entire desktop. Apple’s guide gives separate examples for applications such as Mail, Messages and Safari.
For webpages, read the Safari font-size guide. For document appearance, change the actual document formatting when the saved output must use a different size.
Keep family installation separate
Making text larger does not install a new typeface. Use Font Book installation when an application needs an actual family resource.
Read typeface versus font for the distinction between a design, a resource and a size setting.
Your questions, answered.
Does the Text size setting control every Mac app?
Apple documents supported apps and app-specific options. Some software has its own controls.
Will zoom change the saved document typography?
A viewing-scale change is different from editing the document’s own type settings. Use document formatting when the saved layout needs to change.
Sources & background
Sources supporting this page’s explanations. Practical examples are our editorial suggestions.