A chart of mattress sizes in the United States is available on CSGNetwork.com. The chart contains height and width information for each size, along with the amount of space per person. Comments for each size include extra information. More detailed descriptions of each mattress size are available on BetterSleep.org.
BetterSleep.org includes information about unusual types of mattress, such as futons and crib sizes. The site also features pages on selecting the right mattress, how to maintain a mattress and the various types of construction.
BeddingExperts.com offer a list of text descriptions and diagrams that show how people fit on various mattresses.