To write a lab report, explain what you aimed to find, how you measured it, what you found and what it means, with enough detail that someone else could repeat the experiment.
This page covers each section of a standard STEM lab report, the tense to use, how to present data and uncertainty, example excerpts and a checklist to run before you submit.
The Sections of a Lab Report and What Each Does
A standard lab report has a title, abstract, introduction, method, results, discussion, conclusion and references. The introduction gives the theory and aim; the method makes the work repeatable; the results present data without interpretation; the discussion explains them.
Write the method and results first, while the practical is fresh, and the abstract last.
Lab Report Structure at a Glance
| Section | What it contains | Usual tense |
|---|---|---|
| Title | What was measured, and under what conditions | Not applicable |
| Abstract | Aim, method, key result with a value, conclusion | Past |
| Introduction | Theory, equations, aim and hypothesis | Present for theory, past for your aim |
| Method | Equipment, quantities, conditions and procedure | Past, often passive |
| Results | Tables, graphs, calculated values with uncertainties | Past |
| Discussion | Interpretation, comparison with theory, sources of error | Past for results, present for meaning |
| Conclusion | Main finding and whether the aim was met | Past and present |
| References | Sources in your required style | Not applicable |
Some courses also ask for a risk assessment or an appendix of raw data. Check your handbook for the required sections and word limit.
How to Write a Lab Report, Step by Step
- Title. Be specific: "Effect of temperature on the rate of catalase activity" rather than "Enzyme experiment".
- Introduction. Explain the theory the experiment tests, give the key equations with symbols defined, and end with the aim and a testable hypothesis.
- Method. Describe equipment with sizes and resolutions, quantities with units, conditions and the procedure, in your own words. Name the independent, dependent and controlled variables.
- Results. Present processed data in numbered tables and figures with captions. Show one sample calculation. Give final values with uncertainties.
- Discussion. Interpret the results, compare them with theory or accepted values, assess errors and suggest specific improvements.
- Conclusion. State the main result with its uncertainty and whether the hypothesis was supported.
- Abstract. Write it last: one paragraph, usually 100 to 250 words, including your key numerical result.
Presenting Results and Uncertainty
The results section presents what you found, not what it means. Tables and graphs carry the data; the text points the reader to what matters.
- Put the unit in the column heading, as "Length / m" or "Length (m)", not after every value.
- Give every figure a numbered caption and label both axes with quantity and unit.
- Plot the independent variable on the horizontal axis.
- Show error bars where you have uncertainties, and a best-fit line where theory predicts one.
- Round values to match their uncertainty: 9.72 ± 0.07 m/s², not 9.7183 ± 0.07 m/s².
Never change or leave out data to make results look better. If a point is anomalous, keep it, mark it and discuss it.
Example Excerpts
Method excerpt. "A 0.200 kg mass was suspended from a light inextensible string, and the length from the pivot to the center of the mass was measured with a meter rule (resolution 1 mm). The pendulum was displaced by less than 10° and released. The time for 20 oscillations was recorded with a stopwatch, three times for each of six lengths between 0.300 m and 0.800 m."
Results excerpt. "A graph of T² against L (Figure 2) was linear, consistent with T = 2π√(L/g). The gradient was 4.06 ± 0.03 s² m⁻¹, giving g = 4π² / gradient = 9.72 ± 0.07 m s⁻²."
Discussion excerpt. "The measured value is 0.9% below the accepted 9.81 m s⁻² and lies just outside the uncertainty range, which suggests a small systematic error. The most likely cause is measuring length to the bottom of the mass rather than its center, which would make L too large. That would raise the gradient and lower g, matching the direction of the discrepancy."
Check the numbers in the example: 4π² = 39.48, and 39.48 / 4.06 = 9.72. The relative uncertainty of 0.03/4.06 = 0.74% carries over to g, giving ±0.07 m s⁻². The accepted value, 9.81, lies outside 9.65 to 9.79, so the excerpt is right to look for a systematic error.
Writing a Strong Discussion
The discussion is where most marks are won or lost. A strong discussion answers four questions in order.
- What do the results show? State the trend or value plainly.
- How do they compare with theory? Give a percentage difference and say whether it lies within your uncertainty.
- What caused any difference? Separate random errors (scatter) from systematic ones (a consistent shift), and say which way each would push the result.
- How could the experiment improve? Suggest a specific change tied to a named error, such as "use a light gate to remove reaction time".
"Human error" is not an explanation. Name the specific action and its effect.
Common Lab Report Mistakes
- Copying the method from the lab handout word for word.
- Results with no units or no uncertainties.
- Interpreting data in the results section instead of the discussion.
- Graphs with unlabelled axes or the variables the wrong way round.
- Vague errors such as "human error" or "faulty equipment".
- An abstract with no numerical result.
Lab Report Checklist
- Title states what was measured and how.
- Introduction gives theory, equations, aim and hypothesis.
- Method is repeatable, with quantities, equipment and variables named.
- Tables have units in headings; figures have numbered captions.
- A sample calculation is shown.
- Final values have uncertainties and sensible significant figures.
- Discussion compares with theory and names specific errors.
- Conclusion answers the aim; abstract includes the key value.
- References follow your required style.
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Frequently Asked Questions
It depends on the course. First-year reports are often 1,000 to 2,000 words, and advanced reports longer. Follow your handbook's limit.
Mostly past tense for what you did and found, and present tense for established theory and for what your results mean.
Many departments prefer the passive voice in the method, but some accept the first person. Check your module's guidance.
The results present what you found, in tables, figures and values. The discussion explains what those results mean and why they may differ from theory.
Separate random from systematic errors, estimate their size where you can, say which direction each would push the result and suggest a specific improvement.
Yes. Send your measurements and the lab handout. The report is built around your data, which is never invented or changed.