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Guys in one of my recent interview I was asked about my project and in that he asked me what was the reason behind choosing the font size you have chosen for your app? I wasn't able to give a satisfying answer. Could someone help me how to know what should be the perfect font size?

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    The same method that helps you choose the perfect color. – Rob Jul 11 '19 at 10:26
  • Can you provide the reason why you chose a particular font size? It would also be helpful to show a screenshot of your app to provide some context. – 習約塔 Jul 11 '19 at 18:41
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Legibility!

Font size, weight and colour should reflect its hierarchy as close as possible. When it comes to body text, the most important metric is 'legibility.' For the most body fonts, 14-18 px is ideal with appropriate line-height for clarity.

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    I'll emphasize: "with appropriate line height." Different size type requires an adjustment of the space between lines of text (the pros call it leading) to maintain legibility. Also look at line length. If you're not the one who should choose type size, get yourself a graphic designer. They live and breathe this stuff. – Ken Mohnkern Jul 11 '19 at 17:45
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Ergonomic criteria suggest that the appropriate font size is dependent on the luminance of the display screen and the importance of the information being presented (Sanders and McCormick, 1993). For critical uses (i.e., alarm messages) at 70 cm viewing distance, the font size on a display should be 5.1 to 7.6 mm for low luminance; and 3.0-5.1 mm for high luminance. Bullimore et al.(1992) recommends that alphanumeric character heights should subtend an angle of 20 min of arc, or 4 mm at a viewing distance of 60 cm. (source)

Not particularly a paper that answers the question directly, but this adequately sums up the main points. For screen sizes, these measurements can be converted to points and then to pixels. Mobile phones and tablets are held closer than laptops and desktops.

72 points = 1 inch = 2.54 cm

0.75 point = 1 px

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  • If 72pt = 25.4mm then 4mm = 11.33pt, and 0.75pt = 1px, then 11.33pt = 8.5px. So at 60cm (23.6") away they are reccomending 8.5px font? I think the source is a bit dated if the research was done in '92 (or my math is incorrect which is quite likely). – DasBeasto Jul 11 '19 at 13:49
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    11.33 pt = 11.33/0.75 px = 15.1 px, hahaha... almost there. Yeah these are a little dated. Just wanted to highlight the ergonomic point of view. Thanks for taking the time to check the numbers. – Ren Jul 11 '19 at 20:13
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The UX designer is concerned with legibility, how easily the text can be read and scanned. We, as UX professionals, are concerned about font-size, white space, font/background contrast and perhaps x-height. Ultimately all those issues are considered less for their aesthetic characteristics than for their ease of use for the end-user.

All my UX designs, unless there is an existing style guide, are done in Arial. Why? Because it's up to the graphic team, marketing and business to approve a style guide.

If you're applying to a UX role which encompasses graphic design work then the question "why did you use this font?" may have been appropriate. However if the position is strictly a UX role, and you didn't use an unusual combination on fonts, then a good UX answer would be:

"This is a common font that doesn't draw attention to itself. Under normal business circumstances I would follow the existing style guide."

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    I think this answer is slightly off as the question was about the size of the font, not the font-family. – Ren Jul 11 '19 at 20:29
  • Whoops :) You're correct. – Mayo Jul 11 '19 at 20:30

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