Why 80?

80 characters per line is a standard worth sticking to, even today. OK, why?

Well, back up. Let’s examine the axioms. Is 80 characters per line a standard? Not really, it’s a convention. IBM cards (which weren’t just made by IBM or read by IBM machines) were certainly 80 characters wide, as were DEC video terminals, which Macs etc. emulate. Actually, that’s not even true. The DEC VT-05 could display 72 characters per line, their later VT-50 and successor models introduced 80 characters. The VT-100 could display 132 characters per line, the same quantity as a line printer (including the ones made by IBM). Other video terminals had 40 or 64 character lines. Teletypewriters typically had shorter lines, like 70 characters.

Typewriters were typically limited to \((\mathrm{width\ of\ page} – 2 \times \mathrm{margin\ width}) \times \mathrm{character\ density}\) characters per line. With wide margins and narrow US paper, you might get 50 characters: with narrow margins and wide A4 paper, maybe 100.

IBM were not the only people to make cards, punches, and readers. Other manufacturers did, with other numbers of characters per card. IBM themselves made 40, 45 and 96 column cards. Remington Rand made cards with 45 or 90 columns.

So, axiom one modified, “80 characters per line is a particular convention out of many worth sticking to, even today.” Is it worth sticking to?

Hints are that it isn’t. The effects of line length on reading online news explored screen-reading with different line lengths: 35, 55, 75 and 95 cpl. They found, from the abstract:

Results showed that passages formatted with 95 cpl resulted in faster reading speed. No effects of line length were found for comprehension or satisfaction, however, users indicated a strong preference for either the short or long line lengths.

However that isn’t a clear slam dunk. Quoting their reference to prior work:

Research investigating line length for online text has been inconclusive. Several studies found that longer line lengths (80 – 100 cpl) were read faster than short line lengths (Duchnicky and Kolers, 1983; Dyson and Kipping, 1998). Contrary to these findings, other research suggests the use of shorter line lengths. Dyson and Haselgrove (2001) found that 55 characters per line were read faster than either 100 cpl or 25 cpl conditions. Similarly, a line length of 45-60 characters was recommended by Grabinger and Osman-Jouchoux (1996) based on user preferences. Bernard, Fernandez, Hull, and Chaparro (2003) found that adults preferred medium line length (76 cpl) and children preferred shorter line lengths (45 cpl) when compared to 132 characters per line.

So, long lines are read faster than short lines, except when they aren’t. They also found that most people preferred the longest or shortest lines the most, but also that everybody preferred the shortest or longest lines the least.

But is 95cpl a magic number? What about 105cpl, or 115cpl? What about 273cpl, which is what I get if I leave my Terminal font settings alone and maximise the window in my larger monitor? Does it even make sense for programmers who don’t have to line up the comment markers in Fortran-77 code to be using monospaced fonts, or would we be better off with proportional fonts?

And that article was about online news articles, a particular and terse form of prose, being read by Americans. Does it generalise to code? How about the observation that children and adults prefer different lengths, what causes that change? Does this apply to people from other countries? Well, who knows?

Buse and Weimer found that “average line length” was “strongly negatively correlated” with perceived readability. So maybe we should be aiming for one-character lines! Or we can offset the occasional 1,000 character line by having lots and lots of one-character lines:

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It sounds like there’s information missing from their analysis. What was the actual shape of the data? What were the maximum and minimum line lengths considered, what distribution of line lengths was there?

We’re in a good place to rewrite the title from the beginning of the post: 80 characters per line is a particular convention out of many that we know literally nothing about the benefit or cost of, even today. Maybe our developer environments need a bit of that UX thing we keep imposing on everybody else.