I create a critical software (which affect safety), on the GUI, I need a font that has clarity & clear typeface which is very readable, mostly that font will be displayed at height of ~18px, do you have any suggestion the best font for it?

*added: most important requirement would be:

  1. readable on small size ~18px
  2. distinguishable capital letter O and number zero '0', small letter 'l' and capital letter 'I' or number '1'
  3. looking good on bright over dark background

5 Answers 5


Use a typeface designed for programmers, such as Inconsolata. These have to avoid ambiguity, e.g. between 0,o,O,l,1 etc. They also look great light on dark backgrounds!


To choose a right screen font around us, we can refer to our real world examples to understand this.


Apple’s celebrated “Aqua” interface, used in their OS X series of Operating Systems, is one of the world’s most recognisable, usable and beautiful GUIs available. Undoubtedly, a vital part of the Aqua look is in the font used – Lucida Grande. Such is the popularity and beauty of this font that it has become widely used as the body text font on websites all over the internet. It is, for example, Facebook’s primary font.


And in the world of Microsoft Windows, the release of their Vista OS also introduced a brand new GUI named “Aero” – featuring translucent ‘glassy’ windows, glossy buttons and a brand new system font called Segoe UI which is my favourite can read at a very small font size, legible, readable. Segoe UI is an excellent humanist sans-serif that has proven to be very popular and highly legible to boot. MS continued this font in Win-7 as well.

Some of the best SANS screen fonts






Hope this helps....


Standard fonts that the users are most exposed to will work best for readability. Depending on the type of information you need to display, you would then narrow it down to monospaced, sans-serif or serif fonts.


Good ol' Times New Roman would be unambiguous in a critical application, I think. (No idea if any fonts came to be specially designed for critical applications.)

  • 1
    i think the old TNR has ambiguous letter 'O' and zero '0', number '1' and small letter 'l' or capital 'I'
    – uray
    Commented Dec 8, 2011 at 12:15
  • TNR is not a good choice in my opinion, it's designed to be readable in print, not on screen.
    – fredley
    Commented Dec 8, 2011 at 12:34

So, first, start here:


Set the font size to 18, like you want. What I recommend, after doing this, is Andale Mono (MAC font), or Inconsolata (Google Web Font). Both of them represent zero with a slash or dot in the center. Both of them clearly distinguish between one, lower-l, and upper-I. You can set the background color to whatever you want, and see if they can be read well.

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