Mattres Size

Mattreses come in four basic sizes, and then there are some variations on some of those sizes. First of all, the order of sizes from smallest to largest is

Twin (also called Single)
Full (also called Double)
Queen
King

There's also the Olympic Queen, which you'll rarely see anywhere. It's a bit wider than a standard Queen. And the California King is longer than a standard King, but not quite as wide for some reason.

The Twin and Full are not only less wide than the others, but they are also shorter (less foot room). However, you can sometimes get an extra long Twin.