Is a line segment just a piece of a line, or is there more to it?
In this guide, we’ll show you exactly what a line segment is and how it differs from other geometric figures.
You’ll find easy definitions, related geometry concepts, solved examples, a fun quiz, and answers to common student questions—all designed to help you learn and master line segments.
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A line segment is a straight path between two points with a fixed length.
Unlike a line, which goes on forever in both directions, a line segment has a clear starting and ending point.
Think of a tightrope—it stretches between two poles but doesn’t go on forever. Or imagine the edge of a table—it has two distinct ends. These are great real-life examples of line segments!
In math, we denote a line segment using its two endpoints with a bar over them.
For example, a line segment connecting points A and B is written as \(\overline{AB}\). We can use any two letters, like \(\overline{CD}\) or \(\overline{PQ}\)—as long as we don’t forget the little bar on top!
A line segment can be part of a larger shape. If we connect multiple line segments, they form the sides of polygons like triangles, squares, rectangles, and hexagons.
And what about its direction?
A line segment can go in different directions—it can be straight across (horizontal), straight up and down (vertical), or slanted (diagonal).
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In math, a line segment is often mentioned along with lines and rays. While they may look alike, they each have different properties.
When we know how they are different, we can find them in shapes, pictures, and even things around us!
Line: A straight path that goes on forever in both directions. It has no endpoints and no fixed length. Think of a road that stretches endlessly or the horizon.
Line Segment: A straight path with two endpoints. It has a fixed length and does not go on forever. Think of the edge of a notebook or a crayon.
Ray: A straight path that starts at one point and goes on forever in one direction. Think about a flashlight beam shining into the distance or an arrow flying through the air—they start somewhere but keep going!
Since a line segment has a fixed length, we can measure it just like we measure a piece of string or the side of a book.
But how do we do that in math?
We can use any length measurement system, unit, or tool to determine the length of a line segment.
One simple method is to use a ruler. Place one end of the ruler at the starting point of the line segment and check the number at the ending point—that number tells us its length!
Let's check out an example on the graph.
If a line segment is drawn on a grid or graph, we can count the spaces between the two endpoints to find the length like so:
Now that you know how to measure a line segment, you can try it on your own!
Check out our video guide on graphing points and lines.
The more we practice, the better we get! Let’s work through these examples together and master line segments.
Is this path a line, line segment, or a ray?
Since the line has arrows on both ends, it goes on forever in both directions. Even though points A and B are marked, they do not stop the line—they are just points on it.
A line segment, on the other hand, has two clear endpoints and does not extend beyond them.
So, what we see here is a line, not a line segment, because it never ends!
Count the number of line segments in this shape:
We can see that our trapezoid ABCD has four points (A, B, C, and D). These points form the endpoints of the line segments.
Since a trapezoid has four sides, and each side is a line segment, we have:
\(\overline{AB}\)
\(\overline{BC}\)
\(\overline{CD}\)
\(\overline{DA}\)
So, there are 4 line segments in trapezoid ABCD.
Write all possible line segments in this path:
We can see that our path has four points: P, Q, R, and S.
Since a line segment is a straight path between two endpoints, we can form different segments by choosing any two points.
Let's list all the possible line segments:
\(\overline{PQ}\)
\(\overline{QR}\)
\(\overline{RS}\)
\(\overline{PR}\)
\(\overline{PS}\)
\(\overline{QS}\)
By connecting every pair of points, we found six line segments in total!
Ready to practice what you’ve learned? Try our 2-minute quiz to see how well you know line segments.
When you’re done, check your answers at the bottom of the guide.
1. Which of these is the best definition of a line segment?
A) A straight path that goes on forever in both directions
B) A straight path with one endpoint that extends forever
C) A straight path between two endpoints with a fixed length
D) A curved path with no endpoints
2. Which of the following is NOT a line segment?
A) The edge of a book
B) A pencil
C) A street with a clear start and end
D) A beam of light shining from a flashlight
3. How many line segments can be formed from four points on a straight line?
A) 3
B) 4
C) 5
D) 6
4. Which of these shapes is made entirely of line segments?
A) A circle
B) A triangle
C) A curved road
D) A wavy line
5. How many line segments are in a square?
A) 3
B) 4
C) 5
D) 6
A line segment is one of the building blocks of geometry and shapes. But when learning about it for the first time, students often have questions!
Here are some of the most common ones we hear at Mathnasium of Richardson West.
No, a line segment is always straight. If a shape has curves, it is not made entirely of line segments. However, some curved shapes, like polygons with many tiny sides, can appear curved from a distance!
Yes! In fact, many shapes are formed this way. For example, in a triangle, each endpoint is connected to two different line segments.
No, a line segment can be any length! It can be as short as a centimeter or as long as a highway—what matters is that it has two endpoints.
Not necessarily! Two line segments can intersect, but they do not merge into one. Instead, they stay separate unless one is part of the other.
Yes! Some shapes, like semi circles or mixed figures, can have both straight and curved parts. Only the straight parts are considered line segments.
Mathnasium of Richardson West is a math-only learning center for K-12 students in Richardson, TX.
Using a proprietary teaching approach called the Mathnasium Method™, our specially trained math tutors offer face-to-face instruction in an engaging and fun environment to help students master any math class and topic, including the line segment, usually covered in 3rd grade math.
Students begin their Mathnasium journey with a diagnostic assessment that helps us identify their unique strengths, learning styles, and areas for improvement. Using assessment-based insights, we develop personalized learning plans to guide them to their best path toward math mastery.
Whether your student is looking to catch up, keep up, or get ahead in their math class, schedule an assessment, and enroll at Mathnasium of Richardson West today!
Schedule a free assessment today with Mathnasium of Richardson West!
If you’ve given our quick quiz a try, check your answers below.
Question 1: C) A straight path between two endpoints with a fixed length
Question 2: D) A beam of light shining from a flashlight
Question 3: D) 6
Question 4: B) A triangle
Question 5: B) 4
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