the.com/em
The width of a capital M, used to measure everything but M itself anymore.
means A typographic unit of measurement, traditionally equal to the point size of the font being used (so a 12-point font has a 12-point em), used to size type, spacing, and layout.
from From the letter M itself — in old metal type, the em was originally the width of a capital M cast as a square block, the widest common letter and a handy standard unit for printers. Over time the em unhooked itself from the actual letter and became an abstract measurement tied to font size rather than the M's literal width, which is why the name now outlives the thing it described.
- origin
- named after width of letter M in old type
- css unit
- relative to parent font size, not actual M
- em dash
- borrowed the name, not the width exactly
- nesting trap
- compounds unpredictably when elements nest em in em