Twin is the smaller size in all the bedding sizes. It is perfect for single sleepers or kids. Twin size is also good for bunk beds or for small space rooms . Twin Flat Sheet Size in inches 66 Inches x 96 Inches. Measurements of twin-size bed flat sheet in cm are approximately 168 cm x 244 cm. Twin Fitted Sheet Size in inches 39 inches x 75 inches. Measurements of Twin size bed fitted sheet in cm is approximately 100 cm x 190 cm.