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I'm being told by an experienced BA (> 25 years) that "Numeric numbers are usually totaled therefore should be right justified." And that text should always be left justified.

I have never heard this before now. Is this a true "standard"?

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Numeric numbers as opposed to non-numeric numbers? – Charles Boyung Nov 11 '11 at 14:16
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@Charles Boyung - That's another uncertainty for me. E.G. Sometimes a number is actually stored as a string. Medicare codes usually are of the form "####", but they are identifiers. They are not used for mathematical operations. In some cases they may even have an alpha character appended to the end. So is it a number? – P.Brian.Mackey Nov 11 '11 at 14:26
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@P.Brian I think you have pretty much identified the difference. A number measures or counts something (such as an age, a price, or similar). Something like a medicare code is not really a number even though it looks a bit like one: it's just a string of characters. – Bennett McElwee Nov 13 '11 at 9:57
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what about dates? – Erics Nov 14 '11 at 6:28
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I would assume that non-numeric numbers means "twenty-one" etc. Clearly there's no rule to right-justify these. – moopet Jul 24 '15 at 8:51
up vote 20 down vote accepted

Yes. English text is usually left-aligned. Numbers are normally aligned so that the various places (unit, tens, etc.) are in columns. If the numbers are integers, this just means right-aligning the numbers. If they have decimal fractions, then the decimal places should be aligned, with the units digits all in a vertical line.

This makes it easy to compare the numbers' magnitudes. Mac OS X gets this wrong in the Finder: File sizes are given in abbreviated form, such as 342kB or 6MB. When reading a file listing, it's hard to spot the 342MB file amongst all the 342kB files.

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Numbers should always be right justified if they're to be compared, especially for cash amounts; this keeps the decimal in the same place if the items are rounded the same and makes arithmetic and comparison easy. – Ben Brocka Nov 10 '11 at 20:33
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@Ben Brocka Numbers should be right-aligned only if their fractional parts are a fixed width (for example, cash amounts probably have a decimal point and 2 fractional digits.). But for example, if your list is 2, 14 and 3½ then the numbers should be aligned on the units digit, not right-aligned. – Bennett McElwee Nov 10 '11 at 21:10
    
True, I'm just very used to money being arranged this way, not non-standard decimals/ect, so I hadn't considered – Ben Brocka Nov 10 '11 at 21:29
    
Why not decimal-align them then? – Alex Feinman Jul 27 '12 at 17:30
    
@Alex, I did suggest that in my answer. See also my other comment on handling non-decimal fractions. – Bennett McElwee Jul 31 '12 at 1:21

Yes, this is a "standard". I am >25 too and I know where to look up this guideline :-)

This is guideline 2.3/16 in: Smith S. L., Mosier J. N. (1986) Guidelines for Designing User Interface Software (ESD-TR-86-278), Bedford: The MITRE Corporation | http://www.dfki.de/~jameson/hcida/papers/smith-mosier.pdf

Authors provide references to even more older standards downto 1975.

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Thanks for the link, Ivan. I think your answer is good, consider adding a screenshot so that it can gain more points. – Zoe K Oct 11 '15 at 11:57

Numbers in a table should be formatted so that digits with the same significance are stacked vertically. While this is often described as "right alignment" or "decimal alignment", there's another scenario I've not seen mentioned: values which sometimes include fractions. For example, if one is listing the dimensions of some components, which column is easier to read:

Bizzler     9¾    9¾
Bozzler    12½   12½
Woozler    48-    48
Wizzler    68¼   68¼
Fozzler    97-    97
Fizzler   125-   125
Feezler   325½  325½

Lining up the units makes it easier to judge the relative size of the numbers than it would be if numbers with non-zero fractions were pushed left.

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While I agree that default for numeric should be right-aligned, I think there are some rare cases where left-alignment makes more sense. One example would be Bank Routing Numbers. The following thoughts together made may think they should be left-aligned:

  • They are always 9 digits in length so there is no issue with trying to line up tens, ones columns. Everything stays nicely in line no matter left, right, or even center aligned.
  • They are often prefixed with a zero that actually has meaning so my brain has a hard time not trying to do math on them when they are displayed right-aligned.
  • We aren't trying to perform mathematical operations on then.
  • The right-most digit is a check digit - so worthless for comparison operations. Arguably if we are trying to do comparisons - perhaps the left-most part is more important.

It looks like the ABA agrees with left-aligning for routing numbers - at least they didn't choose to right-align them in their routing number lookup report

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any number that is numeric in nature and a computation is done on it (like a total) then it should ALWAYS be right aligned ALONG WITH its heading. So other numeric number that are just numbers like units, some procedure code, date, etc should be left aligned ALONG WITH its heading.

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Welcome to UX.SE! Can you explain why it's a standard? How did you come to this conclusion? – BDD Apr 29 '15 at 19:31
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"Numeric numbers" should be decimal aligned even if no computation is being done. It helps readers compare at a glance their magnitude. You make a good point about codes, dates, etc., which probably don't need to be right aligned. – Ken Mohnkern Oct 11 '15 at 12:56

Yes, text should be left-aligned when in grids. Text labels, are best right-aligned. Research shows that there is less cognitive strain identifying relationship between text label and field when labels are right aligned. But in grids and charts, left-align.

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Do you have a source for this? – Adam Grant Sep 4 '12 at 18:45
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Clarification, please. What do you mean by "Text labels are best right-aligned"? What kind of labels do you mean? I assume not button labels, which I think work best centered. – Ken Mohnkern Oct 11 '15 at 12:58

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