Calculate the number of granny squares in the transverse rows of the blanket by dividing the width of the blanket by the width of the squares. For example, if the blanket is 60 inches wide and the granny squares are 5 inches wide, divide 60 by 5. The quotient will tell you that the blanket is 12 squares wide. Repeat to calculate the number of squares in the length (longitudinal rows) of the blanket.
Mark the outer border of the pattern on graph paper using a colored pencil and a ruler. Each square on the paper will count as one granny square. For example, if your calculations tell you that your blanket is 12 squares wide and 15 squares long, make your graph-paper pattern 12 squares wide and 15 squares long.
Designate one color of pencil for each different color of granny square. As you design the pattern, color in the squares on the graph paper. The paper pattern allows you to try out different arrangements of granny squares quickly and easily.