Line Graphs

How warm did it get this afternoon? How fast did the puppy grow? When something changes over time, a line graph shows the whole story at a glance. Learn how to read points on a line graph, spot when the data goes up or down, and find the biggest change. Then read, build, and match line graphs of your own.

What a Line Graph Shows

A line graph shows how one thing changes over time. Each measurement becomes a point, and the points are connected in order with straight lines. Following the line from left to right is like watching the data change, one step at a time.

Here's the temperature measured every hour on a Saturday morning. Tap any point to read it.

Tap a point to see how to read it.

Title

Tells you what was measured.

Bottom axis

Shows time: hours, days, weeks, or months. Time always moves left to right.

Side axis and scale

Shows the amount. The scale counts by the same number every time.

Points and lines

Each point is one measurement. The lines connect them in order.

Reading a point works just like reading a bar. Follow the point straight across to the scale on the side. If it lands halfway between two lines, find the number halfway between them. On a scale that counts by 10s, halfway between 60 and 70 is 65.

Up, Down, or the Same

The slant of each line tells you what happened between two points:

Slants up ↗

The amount increased: it went up.

Slants down ↘

The amount decreased: it went down.

Flat →

The amount stayed the same.

Steepest line

The steeper the line, the bigger the change.

Here's one week of sales at a lemonade stand. Pick a button to highlight the parts of the line that match.

Pick a button above.

How much did sales change from Thursday to Friday?

Thursday was 10 cups and Friday was 30 cups.

30 − 10 = 20

Sales went up by 20 cups

To find how much something changed, subtract. Read both points, then take the smaller number away from the bigger one. Look at the direction of the line to tell whether that change was up or down.

Line Graph or Bar Graph?

Line graphs and bar graphs both show numbers, but each is better at a different job.

Bar graph

Compares separate groups, like favorite fruits or pets. The groups don't have an order, so connecting them with a line wouldn't mean anything.

Line graph

Shows one thing changing over time, like temperature through the day. The line shows how you got from one measurement to the next.

A quick test: if the labels along the bottom are times (hours, days, weeks, months, years), a line graph is usually the best choice. If they're names of groups, use a bar graph.

Practice

Three ways to practice: read line graphs, build them yourself, and match graphs to stories.

Read the Line Graph

Check the scale, read the points, and answer the question.

Question 1 of 10Score: 0

Plot the Points

Use the table to build the line graph. Drag each point up or down to the right value, or tap a column to drop the point there. The line connects the points as you go.

Graph 1 of 5Score: 0

Match the Story

Read the story, then pick the line graph whose shape tells the same story.

Story 1 of 8Score: 0