Step 2 e Divide the range by the approximate number of class intervals Generally we will wish to have 7 to 15 class intervals, which is related with sample size. The larger sample size is the more class intervals there are accordingly Department of Health StatisticsDivide the range by the approximate number of class intervals. Generally we will wish to have 7 to 15 class intervals, which is related with sample size. The larger sample size is, the more class intervals there are accordingly. Department of Health Statistics Step 2