One Size Does Not Fit All
I wrote a guest post for SheOwnsIt.com, "Website Design Mistakes That Cost You Money" and mentioned text sizes should start around 18 pixels. Because the majority of the readers are non-techs, I limited my response to pixels and a desktop sizing I would start with. I actually don’t limit myself to just 18 pixels (or necessarily use pixels). I’ll spare you web designer geek speak of more modern sizings like rems, percentages, or ems. (Tap, tap) Hey, did I just lose you there?
Mobile-friendly sites make use of the technique called media queries. Media queries allow you, in a style sheet, to specify instructions to certain screen sizes like a smartphone. Since most smartphones have retina (high resolution) type screens and things look tiny, I amp up the text size just for them.
And the Magic Answer Is…
The answer is: approximately 24 pixels for body copy. You can achieve that with rems, percentages, etc., but that is the fixed size reference that looks readable. Of course this depends on your font, not all display equally. (Got this idea from EmailOnAcid’s blog.)
I apply this technique to both websites and email newsletters (including this one!).
What size font are you using for smartphones on your website or email newsletters?