Hope this is helpful (I know I’m posting this at least a year after the thread was started…).[code pen](http://codepen.io/wootfox/pen/LHohF) to help explain how I determine when to use px vs % for paddings/margins. (Have a look at the details for the description).
Hope this is helpful (I know I’m posting this at least a year after the thread was started…).
> because the padding/margin value is related to the font-size
Why not use em then? It works equally well with `box-sizing: border-box`. Didn’t read the rest of this thread but I think sometimes padding/margin in percentages makes sense, for example if you like some room to breath on big screens, but don’t want to waste too much pixels on small screens.
@CrocoDillon EM is relative to the font-size of the website, in extensive applications or large sites with lots of data its best to stray away from using EM’s. The document relative height will change according to the page being loaded therefore everything would carry an inconsistent feel. Sure you could avoid away from this early in the beginning but then every other person supporting must use the same mindset as you and if you haven’t already figured this out, very rarely do people do anything just like you would. Stick with media queries and % for fluid layouts.