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.
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.

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.

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.

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 asch
. 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 withch
. -
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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