Standard Euro sham dimensions are 26 by 26 inches, though some retailers stock Euro shams that are slightly oversized at 30 by 30 inches. American stores tend to stock the smaller version, while European stores sell the larger ones.
While most standard pillows are rectangular, European pillows---also referred to as Continental pillows---are square and often used as back support while reclining on a bed.
Pillow sizes for rectangular pillows are 20 by 26 inches for a standard-size pillow, 20 by 30 inches for a queen-sized pillow and 20 by 36 inches for a king-sized pillow. Unlike a sham cover, pillows are inserted into one end of a regular pillowcase for most of these styles.