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How to write a first-year science lab report

How to write a first-year lab report section by section, with a sample paragraph for each, tips for figures and tables, and how to report uncertainty.

By the StudyBrix team · · 5 min read · For First-year university and senior high school science students

In short

  • A standard lab report has a title, abstract, introduction, methods, results, discussion, conclusion and references. Your lab manual always overrides general advice.
  • Methods should let someone repeat the experiment. Results report what you found without explaining it. The discussion explains it.
  • Every measured value needs units and an uncertainty, and every figure and table needs a number and a caption.
  • Write the methods and results first, then the discussion, introduction and abstract last.

What goes in a lab report, and in what order

University writing centres in Canada and elsewhere describe nearly the same structure. McMaster's student success centre, for example, lists a title page, abstract, introduction, methods and materials, results, discussion, conclusions, references and appendices, and adds the most important rule first: your course coordinator's instructions take precedence. Some first-year labs ask for only results and discussion; others want a full formal report. Check before you write.

SectionAnswers the questionUsual tense
AbstractWhat did you do, find and conclude, in one paragraph?Past for what you did
IntroductionWhy does this matter and what did you test?Present for theory
MethodsHow exactly was it done?Past
ResultsWhat did you measure?Past
DiscussionWhat does it mean, and how reliable is it?Past and present
ConclusionWhat is the answer to the aim?Past and present

The sample paragraphs below all come from one simple first-year physics experiment: measuring g with a pendulum. The same moves work for a chemistry titration or a biology enzyme lab.

Title, abstract and introduction

A good title says what was measured and how: "Measuring the acceleration due to gravity with a simple pendulum" beats "Lab 3". The abstract is a complete miniature of the report, usually one paragraph. Write it last.

Sample abstract

The acceleration due to gravity was determined from the period of a simple pendulum of length 0.750 m. The time for 20 small oscillations was 34.8 ± 0.2 s, giving a period of 1.740 ± 0.010 s and g = 9.78 ± 0.12 m/s². This agrees with the accepted value of 9.81 m/s² within uncertainty. The main source of uncertainty was the timing of oscillations by hand.

The introduction moves from the general idea to your specific aim. Give the theory you need, define symbols, cite the source if you use one, and state the aim or hypothesis in the last sentence.

Sample introduction paragraph

For small angles, a simple pendulum swings with a period T = 2π√(L/g), where L is the length from the pivot to the centre of the bob and g is the acceleration due to gravity. Measuring T for a known L therefore gives g = 4π²L/T². The aim of this experiment was to determine g using this relationship and to compare the result with the accepted value.

Methods: enough detail to repeat it

Write the methods as a paragraph, not a copied list of instructions. Include equipment with its resolution, quantities you controlled, and how you reduced error. Many instructors want passive voice ("the length was measured"), though some now accept "we". Follow your course.

Sample methods paragraph

A steel bob was suspended from a fixed clamp by a light string. The length from the pivot to the centre of the bob was measured with a metre stick as 0.750 ± 0.002 m. The bob was released from an angle of about 10° and the time for 20 complete oscillations was measured with a handheld stopwatch, starting the timer as the bob passed its lowest point. This was repeated five times.

Results: figures, tables and uncertainty

Report what you found, in order, without explaining why. Raw data usually go in a table; trends go in a graph. Number every table and figure, give it a caption that says what it shows, label every axis with the quantity and unit, and refer to it in the text ("Table 1 shows..."). Check your lab manual for where captions go.

Table 1. Time for 20 oscillations of a 0.750 m pendulum. Mean 34.8 s.
TrialTime for 20 oscillations (s)
134.7
235.0
334.6
434.9
534.8

Uncertainty is the part first-year students most often leave out. Every measured value gets one, in the same units and rounded to match: write 34.8 ± 0.2 s, not 34.8 ± 0.2134 s. When you combine quantities, the uncertainties combine too. For a product or quotient of independent measurements, the relative uncertainties add in quadrature, which follows from the general propagation law in NIST Technical Note 1297. A power doubles the relative uncertainty of that term.

Sample results calculation

Period: T = 34.8 s / 20 = 1.740 s, with uncertainty 0.2 s / 20 = 0.010 s.

g = 4π²L/T² = 4π² × 0.750 / 1.740² = 9.78 m/s²

Relative uncertainty: √[(0.002/0.750)² + (2 × 0.010/1.740)²] = 0.0118

Uncertainty in g: 0.0118 × 9.78 = 0.12 m/s², so g = 9.78 ± 0.12 m/s².

Your course may use a simpler rule, such as adding relative uncertainties directly. Use the method your lab manual teaches and show it once in full. Our physics lab skills page and chemistry lab skills page have more practice with measurement and data.

Discussion and conclusion

The discussion is where the marks are. Compare your result with theory or an accepted value, using the uncertainty to decide whether they agree. Then name the largest real sources of error, say which direction each would push the result, and suggest a specific improvement. "Human error" on its own earns nothing; say what the human did.

Sample discussion paragraph

The measured value of 9.78 ± 0.12 m/s² differs from the accepted 9.81 m/s² by 0.03 m/s², well inside the uncertainty, so the result is consistent with theory. The timing contributed most of the uncertainty: starting and stopping a stopwatch by hand introduces a reaction-time error of roughly 0.1 s at each end. Timing 40 oscillations instead of 20, or using a photogate, would reduce this. The small-angle approximation was reasonable at 10°, where the period is longer than the ideal value by well under 1%.

A conclusion is two or three sentences: restate the aim, give the main result with its uncertainty, and say whether it supports the hypothesis.

Sample conclusion

The acceleration due to gravity was measured as 9.78 ± 0.12 m/s² using a simple pendulum, in agreement with the accepted value. Hand timing limited the precision.

References, appendices and a final check

Cite your lab manual, textbook and any other source in the style your course names. Science courses often use APA or a numbered style; our APA 7 citation guide covers the common cases. The academic writing citation deck helps the rules stick.

  • Every number has units and an uncertainty, with sensible significant figures.
  • Every table and figure is numbered, captioned and mentioned in the text.
  • Results contain no explanations; the discussion contains no new data.
  • The discussion compares to an accepted value or theory and names specific error sources.
  • The abstract matches the final numbers in the report.

Sources

  1. McMaster University Student Success Centre: Writing lab reports
  2. University of Sheffield: How to structure and write lab reports
  3. NIST Technical Note 1297, Appendix A: Law of propagation of uncertainty

General information for study and teaching, not professional, legal or admissions advice. Rules and requirements change: check the official pages linked above. Found a mistake? Tell us and we will correct it. How we write: editorial policy.

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