5em

5em is a CSS length unit that equals five times the font size of the element to which it is applied. As an em-based unit, its exact value depends on the element’s computed font-size and can change with inheritance and nesting.

For example, if an element has a font-size of 16px, 5em equals 80px. If the font-size is 12px, 5em equals 60px. If a child element uses font-size: 1.5em within a parent of 16px, the child font-size becomes 24px; a 5em value on that child would be 120px.

Because em units are relative to the element, sizes defined in ems can compound through nesting. A child’s font-size defined in ems depends on its parent’s font-size, and any em-based values on that child scale accordingly. To avoid cascading changes tied to the root font-size, some developers prefer rem units, which are relative to the root element’s font-size.

Common uses include scalable margins, padding, and widths that visually adjust with text size. However, using 5em for line-height or other vertical metrics can produce excessive spacing if not carefully tested. As with all em-based values, it helps to test layouts across devices and user font-size preferences to ensure predictable behavior.