How to Find Class Boundaries (With Examples)


In a frequency distribution, class boundaries are the values that separate the classes.

We use the following steps to calculate the class boundaries in a frequency distribution:

1. Subtract the upper class limit for the first class from the lower class limit for the second class.

2. Divide the result by two.

3. Subtract the result from the lower class limit and add the result to the the upper class limit for each class.

The following examples show how to use these steps in practice to calculate class boundaries in a frequency distribution.

Example 1: Calculating Class Boundaries

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

Use the following steps to calculate the class boundaries:

1. Subtract the upper class limit for the first class from the lower class limit for the second class.

The upper class limit for the first class is 30 and the lower class limit for the second class is 31. Thus, we get: 31 – 30 = 1.

2. Divide the result by two.

Next, we divide the result by 2. So, we get 1/2 = 0.5.

3. Subtract the result from the lower class limit and add the result to the the upper class limit for each class.

Lastly, we subtract 0.5 from the lower class limit and add 0.5 to the upper class limit for each class:

How to find class boundaries

We interpret the results as follows:

  • The first class has a lower class boundary of 25.5 and an upper class boundary of 30.5.
  • The second class has a lower class boundary of 30.5 and an upper class boundary of 35.5.
  • The third class has a lower class boundary of 35.5 and an upper class boundary of 40.5.

And so on.

Example 2: Calculating Class Boundaries

Suppose we have the following frequency distribution:

Use the following steps to calculate the class boundaries:

1. Subtract the upper class limit for the first class from the lower class limit for the second class.

The upper class limit for the first class is 60.9 and the lower class limit for the second class is 61. Thus, we get: 61 – 60.9 = 0.1.

Example of calculating class boundaries

2. Divide the result by two.

Next, we divide the result by 2. So, we get 0.1/2 = 0.05.

3. Subtract the result from the lower class limit and add the result to the the upper class limit for each class.

Lastly, we subtract 0.05 from the lower class limit and add 0.05 to the upper class limit for each class:

Class boundaries of a frequency distribution

We interpret the results as follows:

  • The first class has a lower class boundary of 55.95 and an upper class boundary of 60.95.
  • The second class has a lower class boundary of 60.95 and an upper class boundary of 65.95.
  • The third class has a lower class boundary of 65.95 and an upper class boundary of 70.95.

And so on.

Additional Resources

How to Find Class Midpoints
Class Width Calculator
How to Calculate Class Width in Excel

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