There are some sites still use odd numbers for font sizes, but why we used "commonly" even numbers?
OR appears on default in selecting font sizes usually at 12px.
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1My groggy mind is saying this this morning. I believe it started as the font size of the standard UNIX terminal at some point back in the day. Someone may prove me wrong, and I should know the answer to this but I'm worn out, beat up, and unmotivated. That's why this is a comment and not an answer. The even sizes are because it's easier to divide to get even numbers than odd ones. – Rob May 14 '19 at 12:50
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6Are we? In my copy of MS Word, for example, the drop-down list for font-sizes reads something like 5, 5.5, 6.5, 7.5, 8, 9, 10, 10.5, 11, 12, 14, 16, 18, 20, 22, 24, 26, 28, 36, 48, 72. So, 1/3 aren't even and almost 1/5 aren't integer, and the even ones are mostly the larger ones where the relative difference between, say, 72 and 73 is negligible. Also, the larger ones are not so much even as they are multiples of 12, which has well-known advantages. And the default size for a second-level heading is 13. The standard font size in the macOS terminal is 11. – Jörg W Mittag May 14 '19 at 16:28
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5@xiota: 12 is the smallest number that can be divided by 1, 2, 3, 4. 60 is the smallest number that can be divided by 1, 2, 3, 4, 5. That's why the numbers 12 and 60 appear so often everywhere: a dozen is a common unit, a shock is a dozen dozen, 12 hours of daylight, 12 hours of night, 12 months, 60 seconds, 60 minutes, 360 degrees. Originally, this allowed common people without mathematical training to divide things amongst themselves without having to deal with fractions … or having to hack up their sheep in thirds. 72 has a similar property: it is 2*2*2*3*3*3. – Jörg W Mittag May 14 '19 at 19:40
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4@JörgWMittag: out of curiosity, is "shock" really a term for 144? I've heard of a "gross" (popularized by Bilbo Baggins), but "shock" is new to me. – Jon of All Trades May 14 '19 at 21:30
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1@JonofAllTrades: Haha, sorry. You are right, it is "gross" both in English and my native German. A "Schock" in German is five dozen (and I don't think it exists in English). There is also a "great gross", which is a dozen gross. – Jörg W Mittag May 15 '19 at 4:55
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The point is a measurement system inherited from traditional print typography. It has had various definitions, much like the inch and foot. With the introduction of PostScript, it has been defined to be 1/72 inch. I don't recall the specific history, but the use of certain font sizes long predates computing. They continue to be used because they work, and there is no pressing need for change.
Apparently, px doesn't really stand for "pixels". Rather, it is defined as 1/96 inch. For traditional displays, which are 96 dpi, a px is equivalent to a pixel. However, for printers and high-dpi displays, it's different. Converting some common point sizes to px, we get:
- 14pt = 14*96/72 = 18.7 px.
- 12pt = 12*96/72 = 16 px.
- 10pt = 10*96/72 = 13.3 px.
The conversion results in fractional pixels that cannot be displayed accurately on standard displays, even with anti-aliasing and sub-pixel rendering tricks. So web designers may choose to round up or down, according to their preference, habit, or copying of stylesheets. (For example, 13.3 rounded up is 14, even. Rounded down is 13, odd.)
This has to do with technical dependency.
There is no "technical dependency" that affects choice of even vs odd pixel sizes.
Just like icon sizes, font sizes or any other fixed dimension in pixels are maintained at even numbers to support scaling.
There is nothing about even vs odd numbers that affects scaling. For instance, 80% of 24 = 19.2; 80% of 15 = 12. However, 75% of 24 = 18; 75% of 15 = 11.25.
... browsers cannot render pixels in decimal.
Huh? My browser works with base 10 just fine.
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8I'm pretty sure by "browsers cannot render pixels in decimal" he meant browsers can't render a non-integer amount of pixels. – Addison May 14 '19 at 15:19
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1"With the introduction of postscript, it has been defined to be 1/72 inch." - Which was not correct, as the actual size of a point is 1/72.27 inches. – Glen Yates May 14 '19 at 15:22
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1@GlenYates: Only in TeX. Like the answer says, everyone had different definitions; the PostScript point is just as "correct" as any other. – Nick Matteo May 14 '19 at 16:56
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2@kundor: Not only in TeX. That's simply the American pica and point. Europe had a different one (Didot), and it's just as correct. And in digital typography, 1/72 is the widespread and ubiquitous definition (even if TeX does it differently, it's only a niche product). – Gábor May 14 '19 at 19:16
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4@kundor: while mathematically true, that's hindsight from our era. Back when it was determined, there was no need to measure that precisely, especially with a unit that described distances visible to the human eye. Yes, there is a very small difference from the eight decimal onwards, true but I really don't think that indiscernible difference is of any consequence. For all practical intents, there are only three significant uints: the Didot (of historical interest now), the American/TeX and the digital one. – Gábor May 14 '19 at 20:31
