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 shoul... [Read Full]
markdown guide
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.


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.


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


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


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.


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.


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.


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


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.


Thanks for these amazing resources.
Stylus seems nifty.
I personally stick to rem, % and occasionally vh & vw.


I always prefer rem once defining the root size in pixels.


Same. However every now and then I do end up using vw & vh too.


vi and vb sound interesting. If I understand correctly, you can base responsiveness on an element, rather than the viewport?


vi &vb` would be helpful for webpages in different languages.

And yes, you can base responsiveness on the parent element size by using %.


I found a small typo in "So the webpages need to by styled" ->... be styled.


Thanks for pointing it out, fixed it.

code of conduct - report abuse