A king-sized pillowcase usually measures 20 by 40 inches while the king-sized pillow measures 20 by 36 inches. As a general rule of thumb, a pillowcase should extend 4 inches longer than the pillow it covers and have a circumference greater by about 2 inches for easy removal.
Each set of king-sized sheets normally comes with two king-sized pillowcases, which constitute the largest pillowcases typically offered. Other pillowcase sizes include the standard pillowcase and the queen-sized pillowcase. A standard pillowcase should measure about 20 by 30 inches while the queen-sized should extend to 20 by 34 inches. The type of bed one uses typically determines the type of pillow he uses. A twin bed usually features standard pillows while king and queen-sized beds use queen and king-sized pillows to accommodate for the extra size.