The Little Known CSS Unit
2 min read
As a Frontend Developer, it is sometimes humbling to know just how much you don't know about the basic building blocks of the web.
The amount of tools and techniques available to us is A LOT! So it's no surprise we often just pick whatever solves our immediate problem and call it a day
Let's take a look at one of those rarely used tools, the CH CSS unit.
CH Unit Definition
According to the spec
A CH unit is the advance measure of the “0” (ZERO, U+0030) glyph found in the font used to render it. (The advance measure of a glyph is its advance width or height, whichever is in the inline axis of the element.)
Translation: One CH is equal to the space one zero character occupies for a given font. So if we write 00, that's 2ch.
All Characters Are Not Equal
Notice how the definition specifically mentions "0" (zero)? That's important because not all characters in a font are equal (except for monospaced fonts e.g. Courier)
Now that we know what the ch unit is, let's consider where it might be appropriate to use it
I asked this question on Twitter before writing this blog post
It's no surprise people suggested using some sort of line break approach, even the source of the image, the nextjs site, uses
<br> tags to create the markup
I've created a simple example to show how we can use
max-width to achieve this by setting the value to the maximum number of characters we want to appear on one line.
- Suitable for dynamic content
- Better than using
pxor other units for paragraph width
- The appearance doesn't change when the font size changes
- It can be a pain counting the number of characters
- Size can be off for Proportional fonts (non-monospaced), which is the vast majority of fonts
Another scenario where the
ch unit might make sense to define width is a fixed-width text input (e.g. year input - 4ch)
ch unit is certainly not what you want to use in most cases, but it really shines where it makes the most sense, character measurement