Base font

Appearance → Customize → Design → Typography → Base font.

The foundation. Every other role either uses this or is measured against it.

Face

System default means the visitor’s own operating-system font stack — San Francisco on Apple devices, Segoe on Windows, Roboto on Android. It is the fastest possible choice because there is nothing to download, and it always looks native.

The alternatives are nine built-in stacks and anything you installed under Appearance → Fonts (how).

For a text-heavy blog, Georgia is the classic upgrade: a serif designed for screens, present on virtually every device, and it costs nothing to use.

Size

16 is the browser default and the right starting point. Sixteen pixels is the size the whole web is calibrated to, and it is what most readers’ eyes are expecting.

Going to 17 or 18 is a legitimate choice for a long-form blog — the extra tenth of a millimetre buys real comfort on a big screen. Below 16 is a mistake: smaller body text is not more elegant, it is just harder to read, and it fails accessibility expectations.

The box takes a bare number as pixels, or any unit you like: 1.125rem, 17px.

Line height

1.5 is the default and a good one. It is the ratio that reads well at 16px over a 620px measure.

• 1.4 — tighter, works with a smaller measure or a condensed face
• 1.5 — the default
• 1.6 – 1.7 — airier; good for a serif at a larger size, or a very long article

Line height and measure move together. A wider column needs more leading to stop the eye losing its place returning to the left margin. If you widen the narrow width, consider 1.6.

Post body copy has its own control

Design → Single post → Post content font governs the text of a single post specifically. It has a face and a responsive size — desktop, tablet, mobile — and its face defaults to Same as base font, so it follows this role unless you break it out.

Use it when you want posts to read a notch larger than the rest of the site while listings, pages and widgets stay where they are. Leave the tablet and mobile boxes empty to keep the desktop size at those widths.

What the base font reaches

Everything not claimed by another role: page content, excerpts, widget text, form fields, the footer, comments. Headings, the menu, the site title, listing titles and the meta line all have roles of their own and are listed under How the font picker works.