Something that has always puzzled me is the fact that when I change the font used in a program, even though in theory the font size is remains the same, the actual displayed size differs dramatically. For example, Inconsolata at 13 looks so much smaller than Source Code Pro at 13, so that I have to set it to 15 to make my eyes comfortable. In another example, Proxima Nova seems to be smaller than Helvetica Neue.

Why do I feel such a phenomenon? Is it only because different fonts have different single-character width, such that some fonts simply look more cuddled together? Or is it actually that font size doesn’t really mean a lot regarding the real size of individual characters (both height and width), and that different fonts might have radically different actual sizes even though the theoretical sizes specified are the same? If that’s the case, then font sizing looks to be a very confusing matter. Why isn’t there a more uniform way to represent the actual size a character is going to occupy on screen so that switching between fonts would be easier?


2 Answers 2


Or is it actually that font size doesn’t really mean a lot regarding the real size of individual characters

Yes. That's the reason.

This is how fonts looked originally:

enter image description here

The type size referred the height of the block of metal the glyph was placed on--not the size of the letter itself.

All fonts at 72 point were cast in blocks of metal 72 points high. But the actual glyphs could be any size (though usually less than 72 points).


The short answer could be: because a pixel isn't a unit of measure and depends of the screen size where you display your design.

The not so short answer should start asking you What do you understand a pixel is? As I mentioned before, a pixel isn't a concrete length magnitude.

The second detail you have to understand is how is build a type. Nowadays a type for us is a simply set of Bézier curves that define the form of a letter. But anciently it was a piece of metal well built and with a 3D body. It's important because from those times come many design decisions that create subtle differences in the proportions of the letters design.

The length, angle, proportion of many of the ascenders and descenders have to do with the ancient metal dimensions. That's the reason why you can have two different fonts in the same size (i.e. 13 pt) and you can see one bigger than other. It's a question of proportion between the parts of the letter and meanly, the lower case height so called x-height.

You should read about typometry or how to measure and comapre typefaces.

  • @Scott Exactly! That's my point. And that's the reason why if you "measure" your typography in pixels, the size will change in each gadget where you display it. You're right, I wrote wrong the idea.
    – Aradnix
    Sep 19, 2015 at 19:19
  • :) Big difference between "is" and "isn't" :) I'll delete my comment .
    – Scott
    Sep 19, 2015 at 19:25
  • @Scott Thanks for the correction, I wrote it bad.
    – Aradnix
    Sep 19, 2015 at 19:35
  • This isn't exactly correct, but close. The size of the pixels is irrelevant. The issue is that the 'size' of a typeface is not necessarily the size of any one particular glyph. Rather it's the size of the bounding box that surrounds all the glyphs.
    – DA01
    Sep 19, 2015 at 20:09

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