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15 CSS Relative units, how many do you know? em, rem, ex, cap, ch, ic...

Bytegasm! on August 18, 2018

If you are reading this, I'm pretty sure you know at least 5 ways of centring HTML elements using CSS. So, 15 options for relative sizing shouldn...

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Daniel Tonon • Aug 20 '18

html {
  /* 1rem = 10px */
  font-size: 62.5%;
}
body {
  font-size: 1.6rem;
}

Now 1rem = 10px for easy unit conversions and the default font size of the site remains at the expected default of 16px. 😁

It also still allows font scaling since it doesn't involve px units.

Supakorn Thongtra • Sep 18 '18

I personally like .625em :)

Bytegasm! • Aug 20 '18 • Edited

Neat. I've seen a lot of devs prefer this. However, I've personally gotten used to 16px.

Here's the article from 2004 where this technique was first introduced.

Daniel Tonon • Aug 29 '18 • Edited

Ok if you really must use px units for fonts then please install this postcss npm plugin into your build process

npmjs.com/package/postcss-pxtorem

Using px units on any font setting on your site is an instant WCAG AA accessibility fail.

w3.org/TR/UNDERSTANDING-WCAG20/vis...

Same goes for things like vw in font size settings. It should be combined with rem in a calc function to ensure that text is still able to be resized.

Anderson • Aug 19 '18

Careful with vh unit. Some mobile browsers have floating toolbar and in this cases if you are using 100vh with virtual scroll, when browsers toolbar is showing your content will be pushed to bottom.

Backo • Aug 19 '18

css-tricks.com/the-trick-to-viewpo...

Bytegasm! • Aug 20 '18

Thanks, however I wish there was a fairly straight forward solution to this problem.

Daniel Tonon • Aug 20 '18

It sounds like maybe the vi and vb units might be the answer to that since it sounds like they are based on parent element dimensions. It's a shame they aren't supported anywhere yet.

Bytegasm! • Aug 20 '18

If I had a dollar for everytime I ran into this issue..

Bob van Hoove • Aug 19 '18 • Edited

This is helpful, thanks :)

I often find myself using em to make a site readable on a widescreen. Something like p { max-width: 40em; line-height: 1.8em } usually does the trick. I've started using Stylus to 'fix' sites I frequent, like Wikipedia.

Pearsonified has a nice article and even a calculator to give you an indication of readable font size : line height : line width proportions.