# Argument in "thebibliography"

I was reading the explanation about thebibliography and was totally confused:

The thebibliography environment has an argument which should be a string at least the length of the widest entry label in the source list. Instead of using the numbers generated by the environment as entry labels, you can specify your own by using an optional argument to \bibitem, but remember to increase the length of the argument to the thebibliography command.

What does "widest entry label" mean? Practically, what should I put as the argument in

\begin{thebibliography}{?}


or is the argument not necessary?

• If you use numeric labels and have less than 10 items, the argument should be a one digit number, usually 9; if between 10 and 99 items, use 99 and so on. Aug 28, 2014 at 10:04
• @egreg Expand that to an answer? Aug 28, 2014 at 10:17
• @egreg If I have 5 items, can I nevertheless use 99? Aug 28, 2014 at 10:23
• @boaten Why should you? With five items and 9 as argument, the numbers will be flush to the left margin, with 99 they wouldn't. Aug 28, 2014 at 10:24
• The "9" or "99" is just taken as a representative width of the bibliography label. Sure, you can specify a representative width larger than that actually needed, but as egreg asks, why would you want to? Aug 28, 2014 at 10:46

The argument to \begin{thebibliography} is used for setting the hanging indentation of the bibliography items.

If you use numeric labels, then the argument should be a single digit (9 is commonly used) if there are less than ten items; two digits (commonly 99) if there are from 10 to 99 items and so on.

If you use symbolic labels (say Xyz12 or XY13) like BibTeX creates with the abbrv style, then you should pass the widest label, for instance

 \begin{thebibliography}{Xyz12}


or whatever abbreviation is the widest.

The correct argument is needed in order to make the labels flush left and the bibliography items to have precise hanging indentation.

Note that BibTeX is able to figure out the widest label when writing the thebibliography environment to the .bbl file.

• sometimes, "alpha" labels for a bibliography are ridiculously wide (usually labels assigned by an author, not ones generated algorithmically). in such a case, it may be appropriate to specify a reference label that is a "reasonable" width, not something that will indent the entries a third of the way across the page because of just one or two very wide labels; most bibliography routines will, in such cases, "run in" the exceptions and leave the indentation at the width of the specified reference label. Aug 28, 2014 at 16:33
• @barbarabeeton I fully agree. Aug 28, 2014 at 16:37