How to
How to make a line graph
A line graph shows how a value changes over an ordered sequence, usually time. The slope tells the story: rising, falling, flat, or turning. Put several lines on one chart to compare trends that share the same unit.
- List the points along the horizontal axis. Each row is one step in the sequence: a day, a month, a year or a trial number. Keep them in order.
- Enter the values. Each series column becomes one line, so adding series is how you plot multiple lines on one graph. Leave a cell empty when a value is missing and the line breaks there instead of dropping to zero.
- Paste instead of typing. Copy the table from a spreadsheet with dates in the first column and press Paste from a spreadsheet.
- Tune the look. Turn markers on for a few points, off for long series. Smooth curves look softer, and they never overshoot your data points.
- Export. Download PNG or SVG, or copy the image straight into a document.
Should the axis start at zero?
Unlike bar graphs, line graphs do not have to start at zero. A line encodes change through its slope, so zooming in on the range where the data lives is usually the honest choice. Temperatures, stock prices and test scores often read better that way. Switch on Start axis at zero when the size of the values matters more than the change.
How many lines is too many?
Up to four lines stay easy to follow. Beyond that, lines cross and colors become hard to match with the legend. If you have more, split them into two charts with the same scale, or highlight one series in a strong color and set the others to a quiet gray with the color squares.
Tip
Turn on Label the last value of each line for reports. Readers usually want the latest number, and it saves them from reading it off the axis.
Line graph or bar graph?
Use a line when the horizontal axis is continuous and ordered, like time. Use a bar graph when the categories are separate things, like products or countries, where a line between them would suggest a trend that is not there. When each point is a separate case, such as one student's study hours and score, use a scatter plot instead and add a line of best fit.
