Why Do CSS Letters Have a Perplexing Size?

The Perplexing Size of Letters in CSS: Unraveling the True Height

Despite the specified font-size in CSS, the actual height of letters often differs from what one might expect. This discrepancy raises the question: what determines the true height of letters in CSS?

A Historical Perspective

Traditionally, the em unit in typography referred to the size of the metal blocks used to engrave letters, with the capital letter M as the determining factor. However, with the advent of digital fonts, this physical limitation no longer applies, allowing font developers greater freedom.

Establishing Standards

OpenType fonts typically set the em size to 1000 units, while TrueType fonts usually use either 1024 or 2048 units. When using EM to specify a font style, the font-size refers to the font's x-height, which is the distance between the baseline and the mean line of the font. This provides a precise method for defining font size.

But Standards Can Be Flexible

Despite the existence of standards, the actual size of glyphs in a font can vary due to:

• The developer's design choices
• Browser rendering variations
• Screen resolution and pixel density

Exemplifying the Discrepancy

Apple's Zapfino script font initially followed the standard for sizing lowercase letters. However, finding them too small, they increased their size significantly, making them approximately four times larger than other fonts for the same point size.

Further Exploration

For a deeper understanding of typography and the intricacies of font sizing, consider exploring the following resources:

• Wikipedia articles: Point (typography), Pixels per inch, Font metrics, Typographic units
• Font development tools: FontForge, FontLab Studio

By understanding the nuances of font sizing, developers can achieve greater control over the visual presentation of text in CSS, ensuring optimal readability and visual appeal on websites and applications.

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