Origin of numerical font weight descriptions in typography

The CSS specification (among several others) establish that, when selecting a font, the font-weight may be described using numerical descriptors ranging from 100 to 900 at 100 increments, where 400 is reserved for the “regular” weight and 700 for “bold” (this article contains an example of a mapping).

Are these numbers assigned merely conventionally or is there some sort of (at least theoretical) numerical relation between, say, stem thickness and advance width which controls the numerical descriptor that a font “ought” to receive (regardless of whether that relation is respected in any particular font)?


The CSS font-weight is influenced by Linotype numbering system. As you can learn from the wiki, every digit in the number describes different characteristic of the typeface and from this point CSS adopted Lynotype in part… The 100 to 900 system works for some fonts, but fails for other, thus you should always check this in advance before using particular values in the CSS code.

Source : Link , Question Author : Wtrmute , Answer Author : Ilan

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