How to Write an Abstract: Types, Parts, Length and a Labeled Example

Knowing how to write an abstract means knowing what a stranger needs to decide whether to read your paper. An abstract is a short, self-contained paragraph that states what the work did, how, what it found and why it matters, in a fixed number of words. This guide covers the two main types, the parts to include, the length conventions exactly as APA Style and university writing centers state them, a step-by-step method, and a full abstract for an invented study, labeled as an example.

What is an abstract?

Readers use the abstract to decide whether your paper is worth their time.

The UNC Writing Center's handout on abstracts defines an abstract as "a self-contained, short, and powerful statement that describes a larger work." Its contents vary by discipline: scope, purpose, results and contents in the sciences and social sciences; thesis, background and conclusion in the humanities. It also says what an abstract is not. It is not a review, it does not evaluate the work, and it is an original piece of writing rather than an excerpted passage.

UNC gives two main reasons abstracts exist: selection, because readers use them to decide whether a longer work is worth their time, and indexing, because databases search abstracts. So use the terms a researcher in your field would search for. An abstract also differs from the thesis statement inside a paper: the thesis states your claim in one sentence; the abstract reports the whole paper, claim included.

Types of abstracts: descriptive and informative

UNC names two main types, descriptive and informative, and mentions a third, critical, as rarely used. The USC Libraries guide to the abstract also lists a highlight abstract, which it says is not a true abstract. Lengths below are quoted as each source gives them.

The parts of an abstract

UNC lists five elements to keep in mind, adapted from Philip Koopman's guide at Carnegie Mellon: the reason for writing (why the research matters), the problem (what the work tries to solve, its scope and its main argument), the methodology (models, approaches or kinds of evidence), the results, and the implications (what the findings change or add).

The APA Style abstract guide for the 7th edition gives a similar list for research papers and suggests usually one to two sentences per topic: key aspects of the literature review, the problem or research questions, the hypotheses, the methods (including study design, sample and sample size), the results, and the implications. For the humanities, the UW Madison Writing Center shows abstracts that lead with the context and the argument rather than a method and data.

UNC adds that every abstract puts the most important information first and uses the same type and style of language as the original, technical terms included. It also says what to leave out: extensive references to other works, information not in the original, and definitions of terms.

How long should an abstract be?

There is no single rule. The figures below are given as each source states them.

APA's guide also covers the format: the abstract goes on the second page under the bold, centered label "Abstract," as a single double-spaced paragraph with no first-line indent. On the line below, APA asks for three to five words, phrases or acronyms that capture the paper's most important aspects, for indexing and search.

How to write an abstract, step by step

1. Finish the paper first

   USC says the abstract "should be written last," and UW Madison advises waiting until after you have drafted the full paper, so that you know what you are summarizing.

2. Reverse outline the paper

   UNC suggests writing down the main idea of each paragraph, then grouping the main ideas of each section into a single sentence. In a scientific paper, that gives you one line each for purpose, methods, results and discussion.

3. Highlight the sentences that carry the paper

   For someone else's work, UNC recommends highlighting the central sentences and phrases, then rewriting them in your own words in a separate document. For your own, mark the thesis and the main finding of each section. Reading a research paper in passes shows where those sentences usually sit.

4. Draft one or two sentences per part

   Follow APA's pattern: problem, method, results, implications. Put the most important information first.

5. Cut to the limit

   UNC's advice is to revise early and often, deleting extra words. USC adds: no catchy opening, no lengthy background, no redundant phrases, and no unexplained acronyms.

6. Check it against the paper

   USC says to confirm the abstract "completely agrees" with what the paper says. Every number and claim in it must appear in the body.

A worked example: an abstract for an invented study

The study below does not exist. It, its numbers and both abstracts were invented for this page to show the structure, and nothing in them should be cited. Imagine a course paper reporting a classroom study on note-taking.

That example runs to about 120 words, well under APA's 250-word limit. Sentence one gives the reason and problem, sentences two to four the method, sentence five the result, and the last two the implications.

A descriptive abstract of the same invented paper drops the results: "This paper compares highlighting alone with highlighting plus section summaries as review methods in an introductory biology course, and describes the recall quiz used to measure the difference." It says what the paper covers, not what it found.

Which tense to use

The sources disagree here. USC says to "always use the past tense" because you are reporting a completed study. UW Madison's annotated samples show the tense changing with the field: present tense for general facts, interpretations and the paper's argument, past tense for previous research and, in the sciences, for the methods and findings of the study. The example above follows that mixed pattern. If your instructor or journal has a rule, use it.

Abstract vs summary

An abstract is a summary with stricter rules: it covers the whole work, follows a set order, fits a word limit, and travels with the paper. How to write a summary covers the broader skill.

Pitfalls

• Writing it first. It describes the paper you planned, not the one you wrote.
• Promising results without giving them. "Results are discussed" belongs in a descriptive abstract only. An informative one states the finding.
• Adding something new. UNC says not to add information that is not in the original work.

Tips

• Read it as a stranger. USC's test: if this were the only part of your paper another researcher could see, would it tell the whole story?
• Keep a word count beside the draft. UNC suggests using your word processor's word count to track length and hit your target.

Writing an abstract is an exercise in subtraction: finish the paper, find the sentence that carries each section, put them in order, and cut until the paragraph fits the limit and still tells the whole story. Check the word limit first; UNC notes it often signals the type. More guides to reading, noting and writing are on the study hub.