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Table of Contents
What are ch and ex?
Using the ch unit
Using the ex unit
Practical Tips
Browser Support
Home Web Front-end CSS Tutorial How to use ch and ex units in CSS?

How to use ch and ex units in CSS?

Jul 29, 2025 am 04:17 AM
css unit of length

The ch and ex units in CSS are relative to font dimensions, with ch equal to the width of the "0" character and ex equal to the height of the lowercase "x". 1. Use ch for horizontal sizing like input widths (e.g., width: 20ch) and readable line lengths (e.g., max-width: 65ch). 2. Use ex for vertical adjustments such as superscripts (e.g., bottom: 0.5ex) or custom underlines (e.g., padding-bottom: 0.2ex). 3. Both units adapt to the current font and size, enhancing typographic alignment. 4. ch is widely supported and reliable; ex has good support but may vary across browsers and fonts. 5. Prefer ch for responsive text layouts and ex sparingly for fine typographic details, ensuring designs scale naturally with text.

How to use ch and ex units in CSS?

The ch and ex units in CSS are relative length units based on the dimensions of a font, making them useful for creating designs that scale with text. Here's how to use them effectively.

How to use ch and ex units in CSS?

What are ch and ex?

  • ch — Equal to the width of the "0" (zero) character in the current font and font size.
  • ex — Equal to the height of the lowercase "x" in the current font and font size.

These units are especially helpful when you want spacing or sizing to align naturally with the text content.


Using the ch unit

The ch unit is great for setting widths, paddings, or margins that match the natural character width of monospaced or proportional fonts.

How to use ch and ex units in CSS?

Example:

input {
  width: 20ch; /* Can comfortably fit ~20 characters */
}

This is commonly used for form inputs to suggest a natural input length without hardcoding pixels.

How to use ch and ex units in CSS?

Another use:

.container {
  max-width: 65ch; /* Ideal line length for readability */
}

This helps keep text lines at a readable width (around 60–75 characters per line), improving readability on large screens.

? Tip: ch is based on the "0" glyph, so it varies slightly between fonts. In monospace fonts, it’s very consistent; in variable-width fonts, it’s an average reference.


Using the ex unit

The ex unit is less commonly used but can be handy for vertical rhythm or aligning elements with the x-height of text.

Example:

sup {
  font-size: 0.6em;
  line-height: 0;
  position: relative;
  bottom: 0.5ex; /* Move up by half the x-height */
}

This helps position superscript text more naturally than using em or px, because it aligns with the lowercase height.

You might also use it in custom underlines or decorations:

.underline {
  padding-bottom: 0.2ex;
  border-bottom: 1px solid;
}

?? Note: ex can be inconsistent across browsers and fonts, and support isn’t as robust as ch. Use it sparingly and test across devices.


Practical Tips

  • Use ch for horizontal spacing related to text: input widths, max-widths for paragraphs, indentation.
  • Use ex for fine vertical adjustments involving text alignment (e.g., icons next to text, custom superscripts).
  • Both units respond to the current font, so they adapt if the font or font-size changes.
  • They are not fixed units — their actual size depends on the rendered font and size.

Browser Support

  • ch: Well supported in all modern browsers (including recent versions of Edge, Firefox, Chrome, Safari). Note: Older versions of IE had bugs with ch.
  • ex: Also widely supported, but behavior may vary slightly.

Basically, ch is more reliable and widely useful, while ex is niche but helpful in typographic fine-tuning. Use them when you want your layout to respond naturally to the text itself — not just the font size, but the actual shape of the type.

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