Find the lower class limit of the class
Find the upper class limit of the class
Find the lower class boundary by subtracting half the gap between classes from the lower class limit
Find the upper class boundary by adding half the gap between classes to the upper class limit
If classes are continuous, class boundaries are the same as class limits
If classes are discrete, use the midpoint between adjacent class limits to determine the boundaries
For integer data, the class boundary is often 0.5 below the lower limit and 0.5 above the upper limit
Use the formula: lower class boundary = lower class limit – 0.5 × smallest unit
Use the formula: upper class boundary = upper class limit + 0.5 × smallest unit