Graphing data
01 // Setting up the axes
A lab graph almost always puts the independent variable on the horizontal x-axis and the dependent variable on the vertical y-axis, because the graph is showing how the measured value responds to the variable you changed. Each axis needs a label with units, and the graph itself needs a title that names both variables.
Choose a scale that uses most of the graph paper without cramming the data into a corner. Find the range of your data first (lowest to highest value), then pick a scale where each gridline square represents a round number like 1, 2, 5, or 10 units.
02 // Line graph or bar graph
- Use a line graph when the independent variable is continuous and numeric, like time, temperature, or concentration — connecting the points shows a trend.
- Use a bar graph when the independent variable is in separate categories, like different liquids, different brands, or different plant species — there is no meaningful value between the bars.
- Never connect the dots on a bar-graph-style comparison, and never leave gaps between bars on a true histogram of continuous data — the graph type should match what the x-axis actually represents.
03 // Building the graph
1. Find your range
Look at your lowest and highest data values on each axis before choosing a scale.
2. Pick a round scale
Choose a scale per gridline square (1, 2, 5, or 10) that spreads the data across most of the paper.
3. Label both axes
Write the variable name and unit on each axis, for example "time (minutes)" or "height (cm)."
4. Plot and connect or bar
Plot each data point, then connect them with a line (continuous data) or draw separate bars (categorical data).
04 // Questions people ask
Which variable goes on the x-axis of a lab graph?
The independent variable — the one the experimenter chose and changed on purpose — goes on the horizontal x-axis. The dependent variable, the one measured as a result, goes on the vertical y-axis.
When should you use a bar graph instead of a line graph?
Use a bar graph when the independent variable falls into separate categories with no numeric value between them, like different liquids or brands. Use a line graph when the independent variable is continuous, like time or temperature.
How do you choose a scale for a graph?
Find the lowest and highest values in your data, then pick a round number per gridline square (such as 1, 2, 5, or 10) that spreads your data across most of the paper without cramming it into a small corner.