When it comes to fonts, size matters a lot. The font size needs to be big enough so that people can read it without strain.
Not just old folks — For older people this is critical. Starting in their 40’s, most people have increasing difficulty reading small fonts. But it’s not just older people that need fonts to be bigger. I’ve conducted many usability tests on web sites and heard people in their late teens and early 20’s make spontaneous comments about the font being too small.
x-height magic — Some fonts can be the same size as others, but look bigger, due to the x-height. The x-height is literally the height of the small letter x in the font family. Look at the illustration at the top of the post to see how the x-height is measured. Different fonts have different x-heights, and as a result, some fonts look larger than others, even though they are the same font point size.
The same but not — Some of the newer font families, such as Tahoma and Verdana, have been created with large x-heights so they will be easier to read on a screen. The paragraphs below show different font families that are all the same size. Some look bigger, however, because of the larger x-height.
What do you think? Do you have trouble reading fonts online? What font types and sizes do you use?