Font Size Converter

A pixel (px) is an absolute unit that does not scale with user preferences. A rem (root em) is relative to the root element's font size, which is typically 16px in browsers unless the user has changed it. Using rem allows text to scale when users change their browser's default font size for accessibility. The conversion: 1 rem = 16px (default), so 1.5 rem = 24px.

Both em and rem are relative units. Em is relative to the font size of the parent element: if a parent has font-size: 20px, then 1em = 20px for child elements. Rem (root em) is always relative to the root element's font size (html element), regardless of nesting. Rem is generally preferred because em values can compound in nested elements, making them hard to predict.

In CSS, 1pt (point) equals 1/72 of an inch. At the standard screen resolution of 96 DPI (the CSS reference pixel), 1pt = 96/72 = 1.333... pixels. So 12pt = 16px and 9pt = 12px approximately. Points are most useful for print stylesheets. For screen layouts, pixels or rem are preferred.

vw (viewport width) is a relative unit equal to 1% of the browser viewport's width. 1vw = viewport width / 100. For example, on a 1200px wide viewport, 1vw = 12px and 5vw = 60px. Using vw for font sizes creates text that scales with the viewport width, useful for fluid typography. The CSS clamp() function is often used with vw to set minimum and maximum font sizes.

Best practice for accessibility is to use rem for font sizes. This allows users who have set a larger default font size in their browser (a common accessibility need) to have that preference respected. Pixels ignore the user's browser font size setting. The W3C WCAG 2.2 success criterion 1.4.4 (Resize Text) requires that text can be resized up to 200% without loss of content or functionality.