In a frequency distribution, a **class interval** represents the difference between the upper class limit and the lower class limit.

In other words, a class interval represents the **width** of each class in a frequency distribution.

The following examples show how to calculate class intervals for different frequency distributions.

**Example 1: Calculating Class Intervals**

Suppose we have the following frequency distribution that represents the number of wins by different basketball teams:

The lower class limit and upper class limit are simply the smallest and largest possible values in each class:

The **class interval** is the difference between the upper class limit and the lower class limit.

For example, the size of the class interval for the first class is **30 – 26 = 4**.

Similarly, the size of the class interval for the second class is **31 – 35 = 4**.

If we calculate the size of the class interval for each class in the frequency distribution, we’ll find that each class interval has a size of **4**.

**Example 2: Calculating Class Intervals**

Suppose we have the following frequency distribution that represents the exam grades received by students in a certain class:

The lower class limit and upper class limit are simply the smallest and largest possible values in each class:

The **class interval** is the difference between the upper class limit and the lower class limit.

For example, the size of the class interval for the first class is **30 – 21 = 9**.

Similarly, the size of the class interval for the second class is **40 – 31 = 9**.

If we calculate the size of the class interval for each class in the frequency distribution, we’ll find that each class interval has a size of **9**.

**Additional Resources**

How to Find Class Boundaries

How to Find Class Limits

How to Find Class Midpoints

What if the class interval is not giving, how do you determine the it, example: 20, 56, 40, 70, etc. How can you determine the upper and lower class limit.

How can we know that a question can be or cannot be divided into ckass interval

This really ease my understanding. Thank you.

I have a data where there were no upper and lower class limit l, but it says I should construct an appropriate distribution table, hence class interval must be necessary how do you think I go about it

Thank you 🙏🏻

How do we find the class interval in a frequency table that has classes with different class intervals?

I didn’t understand that part of frequency, where did you obtain those figures in frequency line