King-size comforters are 110 by 96 inches. That is 30 inches wider than a full-size comforter but only 6 inches longer. A full size comforter will fit into a washing machine that has a capacity of 3.5 cubic feet, but king-size comforters will not fit into a small capacity machine.
A front-loading washing machine with a 4.6-cubic-foot capacity will fit a king-size comforter. A front-loader does not have an agitator, which can twist and pull on the comforter. As the drum turns on the machine, the comforter follows the drum so far and drops back into the water. This is the best way to wash a large comforter and get it clean without stressing the material and batting inside.
King size comforters can be washed in a top-loading washing machine that has a capacity of 4.6 cubic feet. Although the drum size is large, the agitator takes up some space and swishes the comforter back and forth to clean it. The comforter will get clean, but the top-loader is harder on the material and batting than a front-loader.
Laundromats typically have large size front-loading washing machines. These large washing machines have the capacity to wash king size comforters, sleeping bags and draperies. If you use a washing machine at a laundromat, you will also have access to large dryers.
Any size dryer will work for drying a king-size comforter as long as you stop the dryer every 10 to 15 minutes and fluff the comforter, untwist it and reposition it in the dryer. Laundromat dryers are extra large to hold large loads of clothes and can dry a king-size comforter without the need to untwist, fluff and reposition the comforter during the drying process.