Learn how to calculate the IQR of a data set. CALCULATING THE Q1, Q3 AND IQR Step #1: Order the numbers from LEAST to GREATEST Step #2: Identify the EXTREMES Step #3: Find the MEDIAN of the data set Step #4: Find Q3 or the UPPER QUARTILE (this is the MEDIAN of the UPPER HALF of the data). You will only use the data to the right of the original median for this step. Step #5: Find Q1 or the LOWER QUARTILE (this is the MEDIAN of the LOWER HALF of the data). You will only use the data to the left of the original median for this step. Step #6: Calculate the INTERQUARTILE RANGE by subtracting the LOWER QUARTILE from the UPPER QUARTILE.