How to Write a Lab Report: Complete Guide for Science Students

TL;DR

• A lab report has 7 main sections: Title, Abstract, Introduction, Methods, Results, Discussion, and References
• Write your Methods and Results first (while the experiment is fresh), then Introduction, then Discussion, then Abstract last
• The Discussion is where your grade is made or lost — it's where you actually think about what happened
• Keep it concise, use past tense for what you did, and always connect results back to your hypothesis

---

Lab reports are the assignment nobody teaches you how to write. Your professor shows you how to do the experiment, your TA walks you through the data collection, and then everyone just... expects you to know how to turn all of that into a formal scientific paper.

If you've been staring at a blank document with "Lab Report" typed at the top and nothing else, you're in good company. Let's break this down section by section so you can actually finish this thing.

The Structure: What Goes Where

Every lab report follows roughly the same structure. Some professors want slight variations (always check your rubric), but here's the standard format:

1. Title Page
2. Abstract
3. Introduction
4. Materials and Methods
5. Results
6. Discussion
7. References

Some classes also want a conclusion as a separate section, and some combine Results and Discussion. Check your assignment sheet — but even if it varies, understanding each part will get you through it.

The Writing Order (This Is the Secret)

Here's a tip that will save you hours: don't write your lab report in order. Write it in this order instead:

1. Methods → Write this right after the lab while you remember everything
2. Results → Organize your data while it's fresh
3. Introduction → Set up the background and hypothesis
4. Discussion → Interpret what happened
5. Abstract → Summarize the whole thing
6. Title → Now you know what the report is actually about

Writing the Methods and Results first means you capture details while they're fresh. The Introduction and Discussion require more thought, so they come after you've had time to process. The Abstract comes last because you can't summarize something you haven't written yet.

Section 1: Title Page

Keep this simple. Most lab reports need:

• A descriptive title (not just "Lab 4")
• Your name
• Your lab partner(s) name(s)
• Course number and section
• Date the experiment was performed
• TA's name (some profs want this)

Bad title: "Chemistry Lab Report" Better title: "Determination of Caffeine Content in Commercial Beverages Using UV-Vis Spectrophotometry"

Your title should tell the reader what you studied and how. Think of it like a tweet about your experiment — what's the key info someone needs?

Section 2: Abstract (Write This Last)

The abstract is a 150-250 word summary of the entire report. It should cover:

• Purpose: Why you did the experiment (1-2 sentences)
• Methods: How you did it (1-2 sentences)
• Key results: What you found, with numbers (2-3 sentences)
• Main conclusion: What it means (1-2 sentences)

Example: "The purpose of this experiment was to determine the concentration of acetic acid in commercial white vinegar using acid-base titration with standardized NaOH. A 10.0 mL sample of vinegar was titrated with 0.1024 M NaOH to the phenolphthalein endpoint. The average volume of NaOH required was 38.7 ± 0.3 mL across three trials, corresponding to an acetic acid concentration of 0.396 M (4.74% w/v). This value falls within 5% of the manufacturer's stated concentration of 5%, with the lower experimental value likely attributable to slight evaporation of acetic acid from the sample."

Notice: no fluff, no background information, no "this experiment was very interesting." Just the facts, tightly written.

Section 3: Introduction

The Introduction answers three questions:

1. What is the scientific background for this experiment?
2. Why does this experiment matter (or what concept does it demonstrate)?
3. What is your hypothesis?

How to Structure It

Start broad, get specific. Think of an inverted triangle:

• Paragraph 1: General scientific concept (e.g., "Titration is a widely used analytical technique...")
• Paragraph 2: Narrow down to the specific application (e.g., "Acid-base titrations can determine the concentration of unknown solutions...")
• Paragraph 3: This specific experiment and your hypothesis (e.g., "In this experiment, we determined the acetic acid concentration in white vinegar. Based on the manufacturer's label of 5% acidity, we hypothesized that titration would yield a concentration of approximately 0.83 M.")

Common Mistakes

• Writing too much background. Your professor knows what titration is. Give enough context to show you understand the concepts, but don't write a textbook chapter.
• Forgetting the hypothesis. Every intro needs one. Even if your experiment is confirmatory, state what you expected to find and why.
• Using future tense. You already did the experiment. "This experiment will determine..." should be "This experiment sought to determine..." or "The purpose of this experiment was to determine..."

Section 4: Materials and Methods

This is the "recipe" section. Someone should be able to read your Methods and repeat your experiment exactly.

The Golden Rules

Use past tense and passive voice (in most science classes): "A 10.0 mL sample was pipetted into a 250 mL Erlenmeyer flask" — not "Pipette 10.0 mL into a flask."

Be specific with measurements: Not "some NaOH was added" but "25.00 mL of 0.1024 M NaOH was added from a 50 mL buret."

Don't list materials separately unless your professor asks for it. Weave them into the procedure description.

Don't explain why you did each step — that goes in the Introduction or Discussion. Methods is just what you did.

Example Methods Paragraph

"A standardized NaOH solution (0.1024 ± 0.0003 M) was prepared by diluting stock 1.0 M NaOH. Three 10.0 mL aliquots of Heinz White Vinegar were measured using a volumetric pipette and transferred to separate 250 mL Erlenmeyer flasks. Two drops of phenolphthalein indicator were added to each flask. The NaOH solution was delivered via a 50 mL buret until a persistent pink color was observed (>30 seconds). The final buret reading was recorded to the nearest 0.01 mL."

What NOT to Include

• "First, I put on my safety goggles and gloves." (Skip safety protocols unless they affect results)
• "The experiment was done according to the lab manual." (Your professor wants to see that YOU can describe the procedure)
• Any observations or results — those go in their own sections

Section 5: Results

This is where you present your data — but not where you interpret it. Think of Results as "here's what happened" and Discussion as "here's what it means."

Data Tables

Almost every lab report needs at least one data table. Format it properly:

• Number your tables ("Table 1: Titration Data for Vinegar Analysis")
• Label columns with units
• Include uncertainties where applicable
• Put the table title ABOVE the table (this is a science convention)

Figures and Graphs

If your data is visual:

• Number your figures ("Figure 1: Absorbance vs. Concentration Calibration Curve")
• Label both axes with variable name AND units
• Include a caption BELOW the figure (opposite of tables)
• Add error bars if you have uncertainty data
• Use a proper trendline if needed (and include R² values)

Writing About Your Results

In the text, highlight key findings. Don't just say "see Table 1" — point the reader to what matters:

"The average volume of NaOH required to reach the endpoint was 38.7 ± 0.3 mL (Table 1). Using this value, the calculated concentration of acetic acid was 0.396 ± 0.005 M, corresponding to 4.74% (w/v)."

Include sample calculations. Show at least one complete calculation so the reader can follow your math. If you ran the same calculation multiple times, show it once and summarize the rest in a table.

Common Mistakes

• Interpreting data here (save it for Discussion)
• Not including units
• Not reporting uncertainties or significant figures correctly
• Making graphs in default Excel style without labeling axes

Section 6: Discussion (This Is Where Your Grade Lives)

The Discussion is the hardest section — and the one professors care about most. This is where you show you actually understand what happened and why.

What to Cover

1. Did your results match your hypothesis? Start here. Be direct. "The experimental acetic acid concentration of 4.74% was lower than the expected 5%, partially supporting our hypothesis but suggesting systematic error in our procedure."

2. Why or why not? This is the meat. If results didn't match expectations, explain possible reasons:

• Experimental errors (be specific — "random errors" is too vague)
• Limitations of equipment
• Assumptions in your calculations that might not hold
• Environmental factors

3. Error analysis Calculate percent error if applicable. Discuss sources of error — not "human error" (your TA hates this) but specific issues:

• "The buret readings may have been affected by parallax error"
• "Some CO₂ from the air may have dissolved in the NaOH, reducing its effective concentration"
• "The endpoint color change was gradual rather than sharp, introducing uncertainty in the final volume"

4. How do your results compare to known values or other studies? If there's a literature value, compare yours to it. If classmates got different results, mention what might explain the variation.

5. What would you do differently? This shows maturity and scientific thinking. "Future experiments could use a more precise method of endpoint detection, such as a pH meter, to reduce the subjective error associated with color-change indicators."

Discussion Writing Tips

• Use phrases like "This suggests that..." or "One possible explanation is..." — show your reasoning
• Don't blame everything on "human error." Be specific about what could have gone wrong
• Connect back to the concepts from your Introduction
• If your data looks weird, don't hide it — address it head-on. TAs and professors respect honest analysis of unexpected results way more than fabricated-sounding explanations

Section 7: References

Cite your sources in whatever format your professor requires (usually APA or a journal-specific style for science classes).

Common sources to cite:

• Your lab manual or handout
• Your textbook
• Any external references you used for background information
• CRC Handbook or other reference data

If you're struggling with citations, Gradily can help you understand the formatting rules for different styles — just ask it to explain APA or CSE citation format and work through examples.

Formatting Quick Guide

• Font: 12pt Times New Roman or Arial (unless told otherwise)
• Spacing: Double-spaced text, single-spaced tables
• Margins: 1 inch all around
• Page numbers: Top right or bottom center
• Headers: Bold, centered for main sections
• Tense: Past tense for what you did (Methods, Results); present tense for accepted facts ("Water boils at 100°C at 1 atm")

Templates by Subject

Chemistry Lab Report Focus Areas

• Balanced equations for all reactions
• Molar calculations with proper sig figs
• Percent yield or percent error calculations
• Safety data for chemicals used (SDS references)

Biology Lab Report Focus Areas

• Statistical analysis of data (t-tests, chi-square if applicable)
• Diagrams of experimental setup or organisms
• Controls and variables clearly identified
• Ethics statement if working with live organisms

Physics Lab Report Focus Areas

• Free-body diagrams or circuit diagrams
• Uncertainty propagation through calculations
• Comparison with theoretical predictions
• Graphical analysis (slope = physical quantity)

The Most Common Lab Report Mistakes (And How to Avoid Them)

1. Writing Methods as a recipe. Past tense, not imperative.
2. Saying "human error." Be specific or don't mention it.
3. Skimping on the Discussion. This isn't a paragraph — it's usually the longest section.
4. Forgetting units. Every number needs a unit. Always.
5. Making graphs without axis labels. This is an automatic point deduction at most schools.
6. Copying the lab manual's procedure. Paraphrase and describe what you actually did, including any modifications.
7. Not showing sample calculations. Show your work at least once.
8. Writing an Introduction that's too long. 2-3 paragraphs max for most undergrad reports.

Getting Help With Lab Reports

Lab reports combine scientific knowledge with writing skills, which is why they're so tricky. If you're stuck on the science — understanding the concepts behind your experiment, working through calculations, or figuring out what your data means — Gradily can walk you through it step by step.

Understanding the "why" behind your experiment makes writing about it so much easier. When you genuinely know why you added phenolphthalein to that flask, the Discussion section practically writes itself.

And if you're stuck on the writing side, revisit your rubric. Professors usually tell you exactly what they want — they're just not great at explaining how to deliver it. Hopefully this guide bridges that gap.

Now go write that report. Your TA is waiting.