Y-Axis: Definition & Overview

Instructor: Kimberlee Davison

Kim has a Ph.D. in Education and has taught math courses at four colleges, in addition to teaching math to K-12 students in a variety of settings.

The y-axis is the vertical 'ruler' on a Cartesian plane, a two-dimensional graph. Learn why it is important in mathematical graphing and how it relates to describing vertical and horizontal distances.


Imagine you want to measure an object's location vertically using a ruler. The y-axis is like a vertical ruler. It shows you where an object on a Cartesian plane, a two-dimensional mathematical graph, is in the y (vertical) direction. It is also the starting, or zero, point for measuring how far a point is to the right or left (horizontally) on a graph.

Vertical Distances and the y-axis

Suppose you work on the eighth floor of an office building. The elevator can take you up and down to any floor. In fact, someone could figure out what floor you worked on by watching where you got off the elevator.

Elevator on y-axis
elevator on y-axis

In the vertical direction, you work at level 8. In math, the vertical direction is usually called y. So, your office is at y = 8.

Now, unless you are an elevator operator, you don't work right at the elevator. You might work down a hallway somewhere. But, the elevator is the access point to the various floors. Your office on the eighth floor is generally thought of as some distance from the elevator. The elevator is the zero point, or center, of the eighth floor. If you imagine the 20-floor skyscraper you work in, the elevator cuts vertically directly through all 20 floors. It is the orienting line through the center of the building.

Imagine that the eighth floor has one long hallway that extends east-west. One way to describe where your office is on the eighth floor is to say you are six offices east of the elevator. Someone who worked on the elevator would describe their office as being zero away from the elevator. The elevator is the zero point when measuring east-west.

Floor plan with elevator
floor plan with elevator

When graphing on a Cartesian plane, the vertical orienting line is called the y-axis. Like the elevator, it tells you how high or low you are. But, also like the elevator, the y-axis is the place from which you measure your location horizontally (right-left or east-west).

On the graph below, the red dot is at x = -3 and y = 2. The y-axis shows you how high to go to find the y value (2). But it is also the starting point for finding the x-value (-3). The point is three units to the left of the y-axis.

Cartesian plane
Cartesian plane with one point

Crossing the y-axis

Instead of just graphing points, you might graph a line or a curve. In many cases, the line or curve will cross over the y-axis.

curve graphed on Cartesian plane

To unlock this lesson you must be a Study.com Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account