There are three common sizes for lap blanket – small, medium, and large. a. A small lap blanket has a width range of about 24 to 48 inches or (60.9 cm. to 121.9 cm.). b. A medium lap blanket has a width range of about 30 to 50 inches or (76.2 cm. to 127 cm.). c. A large lap blanket has a width range of about 50 to 60 inches (127 cm. to 152.4 cm).