Nothing's worse than buying a new item of clothing and realizing when you get home that it doesn't fit. The same idea applies to buying bedding-you need to be able to choose the right size. While there are some manufacturers that offer custom-sized mattresses, most follow the standard sizing.

Toddler
Toddler beds are used to introduce a child that has usually slept in a crib to sleeping in a normal bed. They are usually smaller than other beds, and often have rails on the sides to prevent the child from rolling out of the bed during sleep. Often you can use the same matteres as the crib so your toile bedding set can be used for a longer timeframe.

Twin
The name sometimes confuses people, but a twin bed is simply the standard size for a single bed. The bedding for these beds is usually the least expensive as it's one of the most common sizes, and not as much material (such as toile or cotton) is used as would be in a double, queen, or king size.

Double
A double bed isn't actually double the size of a twin. It is, however, significantly larger. Still meant for one person, it allows for a little more room. The bedding for this size is slightly more expensive than that for the twin bed.

Queen
Often used by newlyweds or couples on a budget, a queen is larger than the double bed. It comfortably fits two people, but doesn't allow for very much extra room. Bedding for this size is more standard, but can be more expensive.

King
Just like the name suggests, a king bed is the largest available by standard manufacturers. It requires the most material, and therefore is the most expensive. The one factor that keeps the bedding from being overtly expensive, however, is the fact that it's a very typical, standard size offered. One variation of the king size matteres is the California King matteres, that measures seven foot square.