The most common bed sheet sizes are made to fit twin beds and queen beds. Fitted twin sheets measure 39 by 75 inches, and twin flat sheets measure 66 by 96 inches. Fitted queen sheets measure 60 by 80 inches, and queen flat sheets measure 90 by 102 inches.
The other common sizes in North America are extra-long twin, full and king. Fitted extra-long twin sheets measure 39 by 80 inches, fitted full sheets measure 54 by 75 inches, and fitted king sheets measure 76 by 80 inches. Some mattress manufacturers produce a California king size that takes a 72-by-84 inch fitted sheet. Fitted sheets should fit as closely to the mattress as possible and need to be sized for the correct depth of pocket as well as the area of the mattress. Mattresses range in depth from 10 to 18 inches.
Flat sheets don't have to fit a bed as precisely but do need to be wide enough for sleeping comfort. Extra-long twin flat sheets measure 66 by 102 inches, and full flat sheets measure 81 by 96 inches. King and California king mattresses both take a flat sheet measuring 108 by 102 inches.
Standard pillowcases usually measure about 20 by 30 inches. A queen pillowcase measures 20 by 34 inches, and a king pillowcase measures 20 by 40 inches.