: What is the definition of font size? I tried to search the Internet for a definition but I didn't find much. So, what is the definition of font size? For instance, what makes a 10 pixel

@Cofer715

Think of it as the maximum height of a line of text. Glyphs may not be as big as the maximum height, so yeah ... some 10px fonts are not real 10px but 9px or 8px.

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@Caterina889

A font is designed in terms of a design space, typically 1000 x 1000 units for Type 1 and PostScript-derived OpenType fonts, an order of 2 (1024 x 1024, 2048 x 2048, &c.) for TrueType.

A 10 point font is a font set so that the design-space is 10 points (one em-square) wide and 10 points (one em-square) tall, so if one had a font which had a character which completely filled the square design space that character would be ten points wide and ten points tall.

More details on this in any decent text on type design.

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@XinRu324

In Typography the definition for font size is: the size of text characters, measured in units called points (pts); a point is equal to 1/72 inch.

In typography, a point is the smallest whole unit of measure, being a subdivision of the larger pica. It is commonly abbreviated as pt. The point has long been the usual unit for measuring font size and leading and other minute items on a printed page.

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