How many pixels is 1rem?
16px with the browser's default font size. A rem is the root (html) font size, so if a site sets html { font-size: 62.5% }, 1rem becomes 10px.
How do I convert rem to px?
Multiply by the root font size: 1.5rem × 16 = 24px, 0.875rem × 16 = 14px.
What's the difference between rem and em?
rem is always relative to the root font size. em is relative to the font size of the parent element for font-size, and to the element’s own font size for other properties, so it changes with nesting. For em, use the parent's font size as the root size here.
Why do people use rem instead of px?
Sizes in rem grow when a reader increases their browser's default text size, which helps people who need larger text. Pixel sizes stay fixed.