Your customers will be reading a lot of text across your app or site, so how big should the type be?

The days of fixed-size type are long gone. Most browsers on desktop and mobile will let users scale type up and down, switch into "reading mode" and apply system-wide accessibility settings, like large type and high-contrast colors.

With that in mind, all you're doing here is setting the default type size that appears when the product is first opened. Ideally, the type should be big enough to be readable, but not so big as to overwhelm the user or take up too much space in a crowded view.

Body copy in 16px, with a 1.5 line height and "auto" or "default" character spacing, is usually a safe bet and a good default for the vast majority of your users.

Trying to set your own character spacing is usually unnecessary for body copy, because the browser will do a better job of text rendering than you can.