You can see that Twin and Twin XL have a standard width of either 38” or 39”. Also note that the King/Eastern King has a standard width of either 76” or 78”. This will vary by manufacturer. The minimal width difference is not significant when fitting the mattress for bedding.
Most bed frames have standard inside dimensions that directly correspond with the mattress size. Since there are two dimensions for the Twin, Twin XL and Eastern King mattresses, manufacturers default to the larger size for the inside dimension.
Sheets and mattress pads come in standard sizes which correspond to mattress size.
How about pillows? Standard and King are the most popular sizes, but some manufacturers also offer Queen. Dimensions for these sizes are quite consistent across the board.
Standard Pillow 20” x 26”
Queen Pillow 20” x 30”
King Pillow 20” x 36”
Keep in mind that if you choose a Queen pillow, a standard size pillowcase might be a little short in fit, and a Standard pillow in a Queen pillowcase will have extra overhang.
A decorative pillowcase is called a “sham”. There are four main types of shams; European, King, Standard and Boudoir. The sizes noted are for the pillow inserts. Some shams will have a flange, or ruffle, around the edge which adds to the overall size of the pillowcase, but the size of the insert needed stays the same.
European Sham: 26” x 26”
King Sham: 20” x 36”
Standard Sham: 20” x 26”
Boudoir Sham: 12” x 18”
