Device resolution
There are thousands of different devices out there, with millions of potential contexts. We can’t support them all, so we end up choosing a few popular devices, basing our designs on their resolutions, and ignoring the rest of the products on the market. When technology moves on and resolutions increase, our sites will look as outdated as a 600×400 site does now.Pixels
Pixels sizes aren’t constant – or at least the display of them isn’t. 16px text on an iPhone can be ~60% the size of 16px text on a Macbook. Basing designs on pixel measurements creates inconsistency in viewing size across devices and can negatively affect readability and usability.The Device Doesn’t Matter
So how do we do as Mark Boulton suggests and go about designing from the content out? In practice, it means starting with the most common form of content, the paragraph element, and building up to a full layout.It’s tempting to first set the body font size. But the manufacturer or the user has already set the browser’s default size for readability, and we don’t think you should mess with it without good reason.
However, if you base your entire design on this base font size (using ems), then as it increases or decreases, so will your design. Using ems allows your designs to be resolution independent.
Next, use max-width to set the line length of the paragraph to be as readable as possible (~66 characters per line). This will vary from font to font, but something around 30em usually does the trick. This sets the width of your single column layout, making it ‘just right’ for readability.
