The ch unit in CSS represents "character unit", which represents the width of the character "0" in the current font. It is mainly suitable for width layouts based on text size, such as setting the input box width to suit a specific number of characters, creating responsive UI components that are visually aligned with the character width, ensuring that each character is arranged neatly in a code editor or preformatted text block; it performs best in monospace fonts, with 1ch equaling the width of any single character; but in proportional fonts, due to the different widths of each character, it may not be able to accurately align.
The ch
unit in CSS stands for "character unit," and it represents the width of the "0" (zero) character in the current font. It's a relative length unit that helps create layouts based on the actual size of characters being rendered, which makes it especially useful when you want elements to scale proportionally with the text.

When to Use ch
Ideal for Width-Based Layouts That Match Text Size
Using ch
is helpful when you want an element's width to match how much space a certain number of characters would take up. For example, if you're creating input fields or code blocks where the visible width should reflect how much content fits, ch
can be more accurate than using fixed pixels or even em
.
Some typical use cases:

- Setting the width of an input field to fit a specific number of characters.
- Creating responsive UI components that align visually with character widths.
- Code editors or preformatted text blocks where each character should line up neatly.
This works better than just guessing in pixels because the width adjusts automatically if the font changes.
Works Well With Monospaced Fonts
Monospaced fonts — like those used in terminals or code editors — have equal spacing for every character. In these cases, 1ch
equals the width of any single character. This prediction makes ch
especially reliable in environments like <pre class="brush:php;toolbar:false"></pre>
tags or code inputs.

For example:
.code-block { width: 40ch; }
This sets the width of the block to fit about 40 characters from the current monospaced font. If you change the font size or family, the layout still adapts naturally.
Not Always Perfect for Proportional Fonts
With proportional fonts — like most web body text fonts — each character has different widths. Since ch
is based only on the "0" character, it might not accurately represent other letters like "i" or "w." So while it still gives a general idea of character-based scaling, it won't be perfectly aligned with every letter.
Still, for approximately sizing or alignment, it can work fine. Just keep in mind that it's not pixel-perfect in proportional typefaces.
Using ch
can simplify some layout tasks by tying sizes directly to the text itself. It's not needed for every project, but when you need something to look like it was built around character width, it's a handy tool.
The above is the detailed content of What is the CSS ch unit and when to use it?. For more information, please follow other related articles on the PHP Chinese website!

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