There are standard mattress sizes in the USA and most parts of the world. Standard sizes include twin 38 inches x 75 inches, twin xl 38x80, Full 54x75, Queen 60x80, King 76x80, and California king 72x84. There are also some common custom sizes such as short queens at 60x75 or long fulls at 54x80. You can also read our mattress reviews to gain insights.