Default unit for font-size?

Question

Various texts on the net claim that \"pt\" is the default font-size unit when none is provided, however, my own testing seems to demonstrate otherwise. I have read many docu

Answer 1

Per the "CSS Fonts Module Level 3" the font-size property can have values that are:

Value: <absolute-size> | <relative-size> | <length> | <percentage>

<absolute-size>, <relative-size>, and <percentage> are defined in the same spec, and are all either keywords (e.x. small, larger, etc) or have percentage units.

<length> being more generic is defined in "CSS Values and Units Module Level 3":

Lengths refer to distance measurements and are denoted by <length> in the property definitions. A length is a dimension. However, for zero lengths the unit identifier is optional (i.e. can be syntactically represented as the <number> 0).

What this means is that unitless numbers for font-size are invalid, with an explicit exception for 0.

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With that said, what size is <div style="font-size: 20;">20 size</div> being rendered at?

The rendered font-size of an element will depend on a lot of things. However, if we're able to assume that

• the user hasn't customized their default font-size
• the browser is using default styles
• there are no parent elements that would otherwise change the font-size (e.x. <font>, <sub>, <h1>...yes it would be invalid markup to have those elements as parents, but it would still change the font-size)

Then the default font-size in every modern browser that I'm aware of currently is 16px.