What is a PhD thesis? Structure, word limits and rules

A PhD thesis is the long written account of your doctoral research, and it’s the main thing your PhD is judged on. It has to show an original contribution to knowledge in your field. You then defend it in a viva, an oral examination with expert examiners.

How long it is and how it’s laid out depend on your university and your subject. The eight standard PhD limits we found at six UK universities ranged from 65,000 to 100,000 words, but they’re maximums, not targets. Below, we explain what a doctoral thesis must show, what goes in it, the rules you’ll have to follow and what happens once you submit.

What is a PhD thesis?

A PhD thesis, or doctoral thesis, is the single major piece of work that your doctorate is assessed on. The Quality Assurance Agency (QAA), which describes UK degree standards, calls the research project ‘the principal output of a doctoral degree’. Everything else you do, from training courses to progress reviews, leads up to it. Our guide to PhD meaning and doctoral study covers the degree as a whole: entry requirements, how long it takes and what it costs.

Surrey’s guidance notes that many doctoral candidates write their thesis as a monograph: one continuous document in long chapters, each building on the last. That’s the format this guide describes. The other main format, a thesis that includes papers, is covered below.

Is a thesis the same as a dissertation?

In the UK, the written work for a doctorate is usually called a thesis. Oxford’s guidance on writing theses notes that the US swaps the terms. There, a doctorate ends in a dissertation and a master’s in a thesis.

Some UK universities use ‘dissertation’ too: Bristol’s regulations call the PhD document a dissertation. So if your university’s PhD regulations say ‘dissertation’, they mean the thesis. Our dissertation vs thesis guide goes into the terms in more detail.

Do you have to write a thesis for a PhD?

Yes, but its form can vary. The QAA notes that in creative arts the ‘thesis’ may be an artefact and a commentary. And some students write a thesis made up partly of papers written for journals.

Surrey calls this the ‘publication format’, Manchester a ‘journal format thesis’. At Surrey you need your supervisory team’s approval to use it, and there’s no minimum number of chapters that must be papers.

It’s not the same as ‘PhD by Prior Publication’, Surrey’s route for researchers who already have a body of published work. Surrey opens that route only to its own staff and staff of partner organisations. Our guide to the PhD by publication covers that route.

What does a PhD thesis need to show?

Your thesis has to show an original contribution to knowledge. The QAA’s doctoral degree statement says this can come ‘through original research or the original application of existing knowledge or understanding’.

So you don’t need a world-changing discovery. You need a clearly argued piece of research that adds something new to your field and that you can defend. Warwick’s regulations put it this way: a PhD thesis there must be ‘a substantial original contribution to knowledge which is, in principle, worthy of peer-reviewed publication’.

According to the QAA, most doctoral examiners look for work of ‘peer-reviewed publishable quality’. But the QAA adds that this ‘may refer to elements of the thesis rather than the complete work’. In other words, the publishable standard can apply to parts of your thesis, not necessarily the whole document as it stands.

Warwick also expects the work to show ‘a satisfactory knowledge of both primary and secondary sources’. It should include ‘a full bibliography’ and, where appropriate, a description of your methods.

How long is a PhD thesis?

Each university we checked sets a maximum word count, and the standard PhD limits we found run from 65,000 to 100,000 words. What counts towards the limit varies, but all of them leave out the bibliography or references and the appendices.

University	Word limit	What’s left out of the count
Cambridge (Social Anthropology department guide)	80,000 words (about 350 pages)	Bibliography, references and appendices
Cambridge (Department of Engineering)	65,000 words	Title page, declaration, contents, tables, photographs, diagrams, bibliography, appendices and acknowledgements (abstract, captions and footnotes count)
Bristol	80,000 words	References, appendices and lists of contents
Warwick	80,000 words	Appendices, footnotes, tables and bibliography
Newcastle (Medical Sciences; Science, Agriculture and Engineering)	80,000 words	Bibliography and appendices (notes count)
Newcastle (Humanities and Social Sciences)	100,000 words	Bibliography and appendices (notes count)
Swansea	100,000 words for the main text	Appendices, essential footnotes, introductory parts, bibliography and index
UCL Psychoanalysis Unit (one department’s PhD)	100,000 words	Bibliography, appendices and supporting data

Source: each university’s regulations or guidance, checked 27 October 2026. Cambridge’s figures are from the Department of Social Anthropology’s style guide (August 2023) and the Department of Engineering’s thesis page; UCL’s is one department’s page. Newcastle’s integrated PhD programmes have lower limits (80,000 words in Humanities and Social Sciences; 50,000 in Science, Agriculture and Engineering). Links are in the Sources list below.

What this means for you: treat the limit as a ceiling. The QAA points out that a mathematics thesis ‘may be relatively short’, while one in a more discursive subject may run to 100,000 words. It adds that these differences don’t mean different standards, so a shorter thesis in your subject isn’t held to a lower bar.

So is 20,000 words enough? None of the PhD limits we checked is that low, and no regulation we found sets a fixed minimum. Swansea, for example, says there are no set minimum word limits. But it says the maximum for the preceding degree may be taken as a guide.

What matters is whether the work makes its contribution, so check your own regulations and ask your supervisor what’s normal in your field.

Our guide on how long a PhD thesis is covers average page counts, typical chapter numbers and how length differs between subjects.

What goes in a PhD thesis?

Your university sets the parts your thesis must include and the order they go in. Warwick’s rules are a clear example. The front of a Warwick thesis runs in this order:

Title page, with the details listed in the regulations.
Table of contents, listing every chapter, section and appendix with page numbers.
Lists of tables and illustrations.
Acknowledgements, if you include them, thanking the people who helped.
Declaration, a statement that the thesis is your own work, noting any material from collaborative research, earlier degrees or publications (more on this below).
Summary or abstract, which at Warwick should not exceed 300 words.

The chapters that follow depend on your subject and your project. Surrey’s guidance gives a typical shape for a thesis that includes papers; your department’s guidance will say what it expects for a monograph:

an introduction that reviews the literature and sets out your research questions (your PhD literature review is where you show the gap your research fills);
a methodology chapter, if the other chapters don’t cover your methods in enough detail;
the chapters reporting your research;
a discussion or conclusion chapter on what your research contributes.

If you’re in the sciences, your middle chapters may each report a study or set of experiments. If you’re in the humanities, they may be built around themes or arguments instead. Oxford’s guidance notes that how a thesis is organised often varies by discipline, and suggests looking at previously submitted work in your subject.

Your thesis ends with a bibliography or reference list, plus any appendices for material that supports the argument but would interrupt it.

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How should a PhD thesis be formatted?

Your university’s regulations set the format, so check them before you start writing up. Swansea’s thesis guide shows the kind of rules to expect:

Paper: A4.
Font: text normally equivalent to 12 pt Times New Roman, and never smaller than 8 pt.
Line spacing: one-and-a-half, with single spacing for the summary, indented quotations and footnotes.
Margins: 4 cm on the left and at least 2 cm on the right.

Warwick also asks for 1.5 line spacing, apart from the abstract, which may be single spaced.

Language rules vary too. Cambridge’s Social Anthropology style guide says the thesis must be written in English, apart from quotations and recognised technical formulae. Bristol, by contrast, lets students in its School of Modern Languages write in the language of the culture they study. So if you hope to write in another language, check your department’s rules first.

The declaration

Expect to include a declaration: Edinburgh’s and Warwick’s regulations and Cambridge’s Social Anthropology guide all ask for one. At Edinburgh, the signed declaration must state that:

you composed the thesis yourself;
the work is your own or, if you were part of a research group, you made a substantial contribution and it’s clearly shown;
it hasn’t been submitted for any other degree or professional qualification, except as stated;
any publications included are your own work, except where indicated.

Under Warwick’s rules, you can include work already submitted for another degree, such as a master’s. It must be clearly marked in the text, and the declaration must say so. But that material won’t count towards your doctorate.

What happens after you submit your thesis?

After you submit, your examiners read the thesis and you defend it in a PhD viva. The QAA says that in the UK this is usually a closed examination, attended only by you, the examiners and any independent chair or observer. At least one examiner must be external to your university.

Each examiner normally writes an independent report on your work before the viva. The viva then lets them check that the work is yours and that you understand it in depth.

Expect to make some changes. The QAA says examiners often ask even successful candidates for ‘minor’ or ‘major’ amendments, or for resubmission. It describes three to six months for minor changes and six to twelve months for major changes as ‘not uncommon’. But universities define these terms and the time allowed differently, so check your own regulations.

Only a minority of candidates fail outright, and at most universities examiners can award a different degree, such as an MPhil, where that fits better.

Where your thesis goes next

Your thesis may then be made available to other researchers. Manchester, for example, requires final doctoral theses to be made open access within 12 months of submission, unless an exception applies. At Edinburgh, you keep the copyright, but you grant the university the right to publish the thesis.

A thesis is far longer than a journal article, so to publish your research in journals you’ll turn chapters into separate papers. Our guide to turning your PhD thesis into a paper explains how.

PhD theses outside the UK

If you’re studying outside the UK, your own university’s regulations will set the length, format and examination rules. How a doctoral thesis is examined, and what form it takes, can differ between countries:

India: under the University Grants Commission’s 2022 PhD regulations, your institution must complete the whole evaluation of the thesis, including declaring the viva result, within six months of submission. So your result is due within six months of submitting.
Other European countries: some systems use a public defence, which the QAA describes as an event family and friends can attend, where the outcome is usually already known. A UK viva, by contrast, is usually closed.
Sweden and Australia: some universities build the thesis from published papers. At Karolinska Institutet, the compilation thesis is the most common type. At Monash University, a ‘thesis including published works’ is a format of the normal PhD, not a separate degree.

Next steps

Before you start writing your PhD thesis, find your university’s regulations and your department’s guidance. Note the word limit, the required parts and the format rules. Then look at a few recent theses from your department and agree a chapter plan with your supervisor.

If you’re still early in your PhD, a good next step is your literature review, which shapes your whole argument. Nearer the end, turn to preparing for your viva, where you’ll defend your PhD thesis.

Sources