If you are having a king-size bed then you need to have a king-size bed sheet that will fit your bed. King Bed Flat Sheet Size is 102 Inches x 108 Inches. Measurements of king-size bed flat sheet in cm are approximately 260 cm x 275 cm. King Bed Fitted Sheet Size is 78 inches x 80 inches. Measurements of a king-size bed fitted sheet in cm is approximately 199 cm x 203 cm.