Comforters come in many sizes to coordinate with standard mattress sizes. Some variation exists among measurements for each comforter size, so you'll need to know the dimension of your mattress, duvet cover and comforter to ensure that all will correspond with each other before making a purchase. Also be aware of the thickness of your mattress because very thick pillow top mattresses may need a larger comforter.
A few different king bed sizes are sold. The standard king mattress, sometimes known as dual or Eastern king, is 78 inches wide by 80 inches long with comforters typically ranging from 102 inches wide by 86 to 96 inches long. Longer, narrower California or Western king mattresses are 72 inches wide by 84 inches long. The comforter sizes are approximately 102 to 110 inches wide by 96 inches long.
Queen mattresses come in only one size: 60 inches wide by 80 inches long. This size is adequate for many singles, couples and guest rooms. The comforter measurements range from 86 inches wide by 86 inches long to the larger 92 inches wide by 92 inches long.
Full or double mattresses measure 54 inches wide by 75 inches long. While smaller than the queen size, these beds are adequate for a single child, teen, adult or two small adults. Three-quarter beds are even smaller at 48 inches wide by 75 inches long, though they use the same size comforter as the full. Comforters measure 78 to 86 inches wide by 86 inches long.
Twin or single beds are 39 inches wide by 75 inches long; comforters are typically 64 to 68 inches wide by 86 to 88 inches long. This bed size is ideal for children, though a twin XL bed is available that is 5 inches longer. This size is often used for teenagers and in college dorms. The comforter for a twin XL measures 64 to 68 inches wide by 90 inches long. This size will also fit a daybed frame.
If you will be using a duvet cover for your comforter, you may find that purchasing the next larger size of comforter is preferable so that the comforter completely fills the cover. If you do, the comforter should be no more than 2 to 4 inches larger than the cover or you will end up with a lot of extra bulk around the perimeter.