Checking with reputable linen and bedding companies through their online portals is an easy way to find size charts for each company's pillows. Each manufacturer sizes pillows according to its own specifications.
Pillow size options include cot bed, small square, standard, large square, king and queen. Normally, a standard pillow suitable for a twin bed measures about 20 by 26 inches but can be found in slightly larger or smaller sizes depending on the manufacturer.
In addition to different sizes, pillows can be bought with down, synthetic, feather or memory foam filling that provides additional support and comfort for different types of sleepers.