font-relative length
In CSS, 1em equals the computed font size of the element; it therefore has no universal millimetre value without a font-size context.
Converter
font-relative length
ex
exact
- Record
- M550
- Definition quality
- Standardized
- Conversion mode
- contextual
- Calculator
- Context required
Definition
CSS defines ex relative to the x-height of the element’s font; it varies by font even at the same point size.
History & use
It is a digital formalization of a classic typographic concern: how tall lowercase text actually looks, not merely what point size the font claims.
Modern use
Modern use is context-dependent and varies by region or measurement system.
Sources & evidence
Source tier — · confidence high