16px

16px is a measurement used in typography and web design to specify a length of 16 CSS pixels. In CSS, font-size: 16px sets the size of the rendered characters to 16 CSS pixels. The px unit is an absolute CSS length, but CSS pixels are an abstract unit that maps to device pixels depending on screen density and zoom.

In practice, many browsers adopt a default root font size of 16px, making 16px a common baseline for body text. The actual on-screen size can change with browser zoom or device resolution, so the same CSS value may look different across devices or when zooming.

Rem and em are two related concepts. The rem unit is relative to the root element’s font size (often 16px), while em is relative to the font size of the element in which it appears. Because rems cascade predictably, they are frequently used for scalable typography and accessible design.

Accessibility considerations: fixed sentence sizes like 16px can hinder readability for users with visual impairments if the surrounding layout is not adaptable. Modern practice favors relative units and responsive typography, ensuring text remains legible at various zoom levels and on different devices. Users can also increase base text size via browser settings, and well-designed pages respond to that change.

Other uses: 16px is also a common dimension for spacing, borders, and UI rhythm in CSS. It often serves as a design baseline, though the optimal choice depends on legibility, layout, and accessibility goals. See also CSS pixel, rem, em, accessibility, responsive design.