The standard UK pillowcase size is 48 x 74cm / 19 x 29 inches. You can also find king size pillowcases that measure 48 x 88cm / 19 x 35 inches.You might also want a large pillowcase for a memory foam pillow, however you should note that a king size pillowcase will be too long. For a memory foam pillow, you can simply use a standard UK pillowcase.