How Does Line-Height Actually Affect the Vertical Height of Inline Elements?

Inline Elements and Line-Height: Clarifying Vertical Heights

Understanding line-height in inline elements can be perplexing, especially with measurements sometimes deviating from expectations. This article elucidates line-height's impact on different aspects of inline elements.

One source of confusion is the discrepancy between the declared font-size and the height reported by browser developer tools. While font-size approximates the size of characters, it does not account for various factors, including ascenders and descenders, which can exceed the font-size. As a result, inline element heights can appear taller than their font-size suggests.

Another point of contention involves the background color of inline elements. Despite the expectation that it should correspond to the line-height, it often does not. This is because line-height in inline elements defines the vertical space between lines (the line box), not the height of the inline element itself.

To illustrate these concepts, consider the example provided:

#block-element {
  line-height: 15px;
  /* ... */
}

#inline-element {
  line-height: 15px;
  /* ... */
}

For the block-level element #block-element, the line-height determines the height of the box containing both the ascenders and descenders. This box is 15px tall.

For the inline element #inline-element, the line-height of 15px also establishes the height of the line box containing the text. However, the height of the inline element's content area is often measured by the tallest glyph in the font-family and font-size used. In the case of the browser developer tools showing 18px, it suggests that the tallest glyph is 18px tall, exceeding the desired line-height.

In conclusion, inline element line-height calculations consider several factors, such as the font-size, line-height, and glyph heights. Understanding these nuances helps in accurately predicting and adjusting the vertical spacing of inline elements.

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