Locate the middle number in your data set or calculate the average of the two middle numbers if there is an even number of values. The number becomes the median or middle of the box plot. The box plot, also known as the whisker plot or five number summary, looks like a box with a line down the middle to represent the median or middle value.
Draw the ends or sides of the box at the first and third quartiles. A quartile or quarter represents 25-percent of the data values, so draw quartile one or Q1 corresponding to the first end or side of the box at the cut-off point for the bottom 25-percent of the data values. Draw quartile three or Q3 corresponding to the last end or side of the box at the cut-off point for the top 25-percent of the data values.
Identify the lowest and highest value of the data set. Mark these values with an x or a dot, and connect these values to the ends or sides of the box with a straight line.