- Wondering what it takes to complete a PhD? We’ll give you the short answer: a PhD thesis that’s based on original research.
- A PhD thesis has several sections, like an Introduction, Literature Review, Methodology, Results, Discussion, Conclusion, and Bibliography.
- In this article, you’ll find out all about what a PhD thesis is and how to actually write one.
Earning a PhD isn’t just about being smart or ambitious; it’s about completing one major task: writing your PhD thesis. This is where you prove your expertise through original research, showing the world you’ve got something new to say in your field. From choosing your topic and writing up your findings, to defending your work in front of experts, this guide breaks down every step of writing a PhD thesis, plain and simple.
PhD thesis definition
A PhD thesis is the final research project you need to complete your Doctoral degree. It involves advanced, original research that adds something new to your academic field. You need to make an original contribution to your chosen field, not just summarise or discuss previous publications. This makes PhD theses more extensive than Master’s theses.
A quick note on terminology: The meaning of thesis vs dissertation is different in British and American English. In British English, “thesis” is used for a PhD final project, and “dissertation” for Bachelor’s or Master’s projects. In the US, it’s the other way around: “thesis” is for Bachelor’s and Master’s, and “dissertation” is for PhD.
Term | UK Usage | US Usage | International Usage (mainly Europe and beyond) |
Thesis | Refers to the final project submitted for a PhD (doctoral level) | Refers to the final project for Bachelor's or Master's level | Typically used for PhD research work in Europe (e.g. Germany, Netherlands, Scandinavia). Most non-English-speaking countries follow the UK convention. |
Dissertation | Used for final projects at Bachelor's or Master's level | Refers to the final project submitted for a PhD | Infrequently used. In some European countries, it may refer to any academic thesis, but usually aligns with UK definitions in formal academic settings. |
How long is a PhD thesis?
The length of your PhD thesis will depend on your field of study and university requirements. Here are some examples from the University of Sheffield in the UK, so you have clearer expectations.
- Arts and Humanities: around 75,000 words
- Health: around 75,000 words (for both PhD and MD)
- Science: around 80,000 words
- Social Sciences: around 75,000-100,000 words
In terms of pages, you're looking at roughly 200-400 pages, though this can vary based on formatting, figures, and tables.
What should a PhD thesis include?
Here's what you’ll typically include in a PhD thesis and what each section is for:
Section | Academic purpose and technical function |
Introduction | Introduces the research problem, states the main research question(s), outlines objectives, and explains the thesis structure. Frames the scope of the study and justifies its significance. |
Literature review | Critically analyses existing academic work relevant to the topic, identifies research gaps, and positions the thesis within current scholarly debates. Demonstrates depth of knowledge and theoretical grounding. |
Methodology | Details the research design, methods of data collection (qualitative, quantitative, or mixed), sampling strategies, ethical considerations, and data analysis techniques. Validates the reliability and rigour of the approach. |
Results | Presents raw findings, data sets, tables, graphs, and statistical or thematic analysis. Focuses on reporting the outcomes without interpretation. |
Discussion | Interprets the results in relation to the research questions and existing literature. Discusses implications, acknowledges limitations, and offers critical insights. |
Conclusion | Summarises the main findings, highlights the original contribution to knowledge, and suggests future research directions. May also reflect on the research process. |
Bibliography | Lists all cited academic sources using a specific referencing style (APA, MLA, Harvard, etc.). Ensures academic integrity and transparency. |
How many research questions should a PhD thesis have?
Most successful theses focus on 1-3 main research questions. Having too many questions can distract your focus and make it difficult to provide a thorough analysis.
How to write a PhD thesis (step by step)
Here’s a step-by-step guide to help you stay on track and make your PhD thesis more manageable:
1. Choose your research topic and supervisor carefully
First things first, when choosing your PhD topic, consider your interests, the relevance of the topic, and your future career plans. Don’t forget that you’ll spend 3-4 years reading, researching, and writing about that topic. That’s about the same time it took you to get through high school, but now, you’ll focus on one big project
Before you apply for PhD programmes, research potential supervisors. A good way of doing this is by browsing academic articles in your field and checking university staff pages. You’ll often find their email addresses on these pages, so you can reach out to see if your PhD plans align with their expertise.
2. Stay organised with your research
Depending on your field, you may need to conduct experiments, do literature reviews, analyse texts, or interview participants. In any case, you’ll need to work with large amounts of data, so make sure you have appropriate systems to stay organised. Some students find reference management software like Zotero or Mendeley useful.
3. Structure your thesis very well
PhD theses usually include sections like Introduction, Literature Review, Methodology, Results, Discussion, and Conclusion. Yours will likely follow this structure but also include field-specific subheadings.
For example, in a PhD in Psychology, a thesis on “The Impact of Social Media on Adolescent Self-Esteem” might include specific subheadlines for different social media platforms.
4. Write consistently
Writing nearly 100,000 words may seem overwhelming, and rightly so! Try breaking this number down into smaller steps. You could set yourself a daily word count goal, outline chapters in advance, or co-work with a fellow PhD student to make the task more approachable.
5. Be ready to revise again and again
You’ll likely go through several rounds of edits, whether it’s fixing clarity, responding to feedback, or updating your work as your research evolves.
6. Seek and incorporate feedback
Check in regularly with your supervisor throughout the writing process. Their feedback will help you refine your arguments, spot gaps, and improve clarity.
What comes after writing your PhD thesis?
Also known as viva voce, your thesis defence is the final step of your PhD. This is an oral examination where you’ll present and defend your research in front of a panel of experts. While the exact schedule may depend on your field and the country you’re studying in, here’s how it usually goes:
- You'll give a brief presentation summarising your research
- Examiners will ask questions, both general ones (how you came up with the project, how you measured results) and detailed ones (related to the topic)
- Questions may challenge your assumptions, explore alternative interpretations, or test the depth of your knowledge
To prepare, start by understanding what’s expected of you. Do you need to prepare a PowerPoint? How long will the questions last? Is there a way you can prepare in advance? Then, prepare sample questions and answer them out loud.
Stephen Hawking’s PhD thesis: a famous example
Curious to see a real example? Stephen Hawking’s PhD thesis, Properties of expanding universes. This thesis revolutionised cosmology and is one of the most famous of all time. It is also a very good example to use here, because it ticks all the right boxes:
- Original contribution to the field: The thesis proposed that singularities apply to the entire universe. This supported the Big Bang theory.
- Review of literature and theory: There are mentions and analyses of other scientists’ work, including Einstein’s and Penrose’s.
- Clear structure: There’s a clear research question, mathematical methods, and a detailed analysis.
- Forward-looking: The thesis opened up new questions and directions for future research.
- Independent thinking: By reading it, we can see how Hawking contributed to the field and shaped it.
Some other famous PhD theses
It’s surprisingly easy to find full PhD theses online; many universities publish them in open-access repositories. Below you’ll find a few other famous examples. In fact, when writing your own, it’s essential to read a few relevant examples in your field to understand the structure, depth, and expectations.
Scholar | Thesis (with link) & Year | Why was it revolutionary |
Marie Curie | First detailed study of radioactive substances; established the field of radiochemistry and led to the discovery of radium and polonium. | |
Albert Einstein | Used Brownian motion data to confirm Avogadro’s number—offered strong empirical proof of atomic theory. | |
Iván Sutherland | Sketchpad: A Man‑Machine Graphical Communication System (1963) | Laid the foundation for GUI and computer-aided design (CAD); first interactive graphical computer program. |
Max Weber | Linked religious beliefs to economic behaviour; sparked economic sociology by arguing the cultural roots of capitalism. | |
Jocelyn Bell Burnell | Her PhD work led directly to the discovery of pulsars, key to modern astrophysics and understanding neutron stars. |
Your PhD journey starts here!
Writing and defending your PhD thesis will be one of the biggest milestones of your academic life. But it all starts with choosing the right PhD programme.
Start your PhD journey today. Use PhDportal to explore 19,000+ PhD programmes worldwide. Set filters for your destination preferences, budget, and preferred subjects, and we’ll match you with the best programmes.
FAQs
1. How long is a PhD thesis?
Most PhD theses are between 70,000 and 100,000 words, but it depends on the subject and university.
2. How many research questions should a PhD thesis have?
There’s usually one main research question, supported by 1-2 sub-questions.
3. What happens during a PhD thesis defence?
During a PhD thesis defence, you present your findings, answer questions, and show how your research fits into your field.
4. Can I read Stephen Hawking’s PhD thesis online?
Yes, Hawking’s PhD thesis is available for free on the Cambridge University Library website.
5. What is the difference between a PhD thesis and a dissertation?
In the UK, “thesis” refers to the PhD paper. In the US, “dissertation” is used for the same thing.
