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How To Find Class Width?

TopClass width of a class containing data items can be obtained by subtraction of lower limit from upper limit. For example: Class width of class 10 - 20 is 10.

Formula to Find Class Width:

The formula to find the class width is given below:
 
Class width = $\frac{\text{Max value - Min value}}{\text{Number of classes}}$.

This formula is applicable if we have to plot a frequency distribution, frequency polygon, relative frequency, ogive etc. Now, we will see how to find the class width.

Steps to Find Class Width:

Given below are the steps to find class width:

Step 1: First, take some data items to find the class length. We know that class width in frequency distribution can be obtained by subtracting lower class limit from upper class limit. Suppose we have some classes.

0 - 9
10 - 15
16 - 22
23 - 33
34 - 45
46 - 59.

Then, class width of the given data items can be calculated as shown below.
 
Step 2: Using definition of class width, we can find the class width of the above data items.

0 - 9 = 9 (lower limit - upper limit),
10 - 15 = 5
16 - 22 = 6
23 - 33 = 10
34 - 45 = 11
 
Suppose we have some values:
15, 45, 30, 14, 17
16, 44, 31, 29, 24
19, 12, 41, 33, 35.

Then, let us find the class width of the given data using 5 classes.

The formula to find the class width is given as follows:

Class Width = $\frac{\text{Max value - Min value}}{\text{Number of classes}}$.

Here, in the given data items, max value is 45 and min value is 12. Now, put these value in the formula.
On putting values in formula, we get:

class width = $\frac{45 - 12}{5}$

class width = $\frac{33}{5}$ = 6.6

So, we get value of class width = 6.6

This is how we find class width in different cases.