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One of the reasons for using em measurements (especially for mediaquery widths) is based on the fact that we should allow the user to alter their font size to suit them -- either by zooming their browser in/out or using a custom stylesheet. While I don't disagree with this, it seems to me that this will be a very rare user... I'm curious if there are any reliable statistics on the # of people who alter the default browser font size (typically 16px)?

Somewhat related article: http://codeboxers.com/em-vs-px-vs-rem-in-media-queries/

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I suspect that users who adjust the browser's default font-size has gone the way of the dodo due to all of the knuckleheads designers who insist using px values combined with the fact that this setting has been buried in the browser's configuration. Users have been trained that this setting does nothing in their browser, so why bother touching it? –  cimmanon Jan 17 at 21:14
    
^ Yes, I was thinking the same thing w/r/t that rarely-used browser setting. Although it is easier now to Ctrl-+/- or Ctrl & mousewheel to alter the zoom in most browsers. I wonder if the average user makes use of this, or just us web developers. Would be nice to see some #s on this... –  Luke Jan 17 at 21:19

2 Answers 2

There are statistics available, but they vary. This site says 88.9% of users have 16px as their default, this site says 99.7%.

But it shouldn't matter.

If you design a web page, you have two options: either leave the user's preference intact, that is, don't change the font size at all, or choose your own font size. That's it.

If your decision depends on whether the user's preferred font size is 14 px or 16 px, you're doing it wrong.
If you set the font size of html to a percentage of the user's preference, you're doing it wrong.
And if you say it doesn't matter because the user can zoom anyway if they don't like your font size, that's not good either!

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Some interesting points there. One issue though is that the first link you point to is from 2006 (they were still measuring user font preferences of users with IE5!) and the other link doesn't have any date against it at all, so no idea how accurate these figures are today. Doesn't mean these findings aren't useful though, just that they're not the freshest they could be. –  JonW Jan 23 at 9:32
    
Thank you for the links. Too bad we don't have anything recent from a very reliable source. The reason I'm wondering what the percentage of users who have different than default settings is because it is sometimes recommended to use em to measure their mediaquery break points (rather than px), but this can vary if the user has overridden the default font size. –  Luke Jan 23 at 22:03
    
Setting breakpoints depends on what you want. If you want to target mobile phones with a screen width of 320px, then use 320px. If you want, say, to avoid lines of text wider than 50em, use 50em. There is no need to treat browsers with a font size of non-16px as a special case. You can think in ems, or you can think in pixels, but you can't think in "ems, unless an em is not 16 pixels". That is not the right mindset. –  Mr Lister Jan 24 at 6:03

Bear in mind accessibility requirements are a factor too.

http://www.w3.org/WAI/intro/accessibility.php

Within the visual impairment category (including increases in age of users), there are users who will make font size bigger.

ome earlier stats (U.S.) are here: http://www.afb.org/info/blindness-statistics/statistical-snapshots-archive/computer-related-statistics-archive/technology-and-computers-computer-use/2345

Besides being the right thing to do to accommodate users, legally you may be required to, also. There are lots of accessibility features now in software. E.g., http://msdn.microsoft.com/en-us/library/windows/desktop/bb545462.aspx

And for mobile UIs too (e.g., https://www.apple.com/accessibility/ios/).

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Stats on total visual impairment isn't too helpful because the solutions they use may be different: blindness or bad impairment use screen readers whereas other impairments might require larger text or color changes. Also, some people not classified as visually-impaired may be altering their font size. –  Luke Jan 17 at 22:18

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