How many references on average are typical for a PhD Thesis?

More specifically, I'm looking for a comparison of the average number of references for an engineering PhD thesis and PhD theses in other fields.

I'm looking for references or data on the subject.


As alluded to in the comments, there is no generic "right" answer: the number will depend strongly on the nature of your thesis, the state of the literature related to it, and your personal scholastic style. Nevertheless, in the spirit of engineering approximations, I will supply you with some rough guidelines.

  • As a lower bound, I would be startled if it was possible to place most theses within the context of pre-existing work in less than about 20 references. In certain contexts such as an obscure corner of pure mathematics perhaps this might be possible, but in most cases work does not take place in a vacuum, and other people will have either used similar techniques or cared about similar problems in the past.

  • As an upper bound, I would be concerned with a thesis with on the order of 200 or more references that the student hasn't been doing enough work on their own original research and has been investing too much time and energy in building a literature review, rather than a thesis. Again, there will likely be cases where a thesis with an extremely high number of references would be reasonable, but these are likely to be unusual.

Notice the extremely wide range and suspiciously round numbers in my estimates: really there is no "right" answer for how many there should be in general, but perhaps these will help with some initial first impressions in one's thinking.

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    "upper bound... 200 or more": In a corpus of PhD theses in Agricultural Botany or Agricultural and Food Economics at the University of Reading, average number of citations per thesis were 248.8 and 333.5, respectively. (Source) (I don't know how many unique references these citations were to, though) – ff524 Sep 21 '15 at 3:15
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    "lower bound...less than about 20 citations": as a fun data point, John Nash's PhD thesis had 2 references. – ff524 Sep 21 '15 at 3:39
  • @ff524 Apologies for any confusion between citation and reference in my original writing; I've clarified. The citation data point is interesting, but doesn't answer the references question---I certainly tend to see many citations to key references. Nash, I would definitely count as an unusual data point. :-) – jakebeal Sep 21 '15 at 3:46
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    I think your upper bound is too low. In energy studies, I expect to see 150-250 references. 200 is not unusual for a lit review. – EnergyNumbers Sep 21 '15 at 6:22
  • Nash referenced two other sources - one of which his own. :D – fgysin Sep 21 '15 at 9:32

In essence, the number should be small enough to prove that the major composition of your thesis is your own work, yet large enough to satisfy the committee during your thesis defence.

As first stated, there is no actual upper or lower bound per se. But required number of items to be referred is more of a hidden factor that is highly dependant on your doctoral committee. Thus it would be best to consult your advisor and, if permitted so, members of your doctoral doctoral committee. In addition to that, you ought to look through some PhD dissertation accomplished by others in your field to get a good idea of the average number if that is what you really want.


A quick look at the mostly Mechanical Engineering theses I have on my computer at the moment gives an average of just over 100 references, with a range of approximately 80-150.

I haven't been able to find any quantifiable data but I feel this is about right. Some people will have significantly more and a few less.

I also suspect there is significant variations between subjects with arts and social sciences having significantly more references and more theoretical subjects having slightly less.

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