Your interest in the LG - SteamWasher 4.0 Cu. Ft. 9-Cycle Ultralarge-Capacity High-Efficiency Steam Front-Loading Washer, Model # WM3250HWA is greatly appreciated. Thank you for contacting us with your question concerning whether or not this washer is big enough for a King size comforter.
The answer for that is not quite so simple only because there are so many different fills that are used in comforters making their respective weights very different. So allow me to answer your question this way. 4.0 cu. ft. is a large capacity and can hold from 14-16 lbs of washing, but that is wet clothing! As you and I know, wet clothing can be extremely heavy, especially a comforter!
Knowing the weight of your comforter will definitely help, fold it up and put it on a scale and weigh it! How much water soaks it is the key and if it appears that your comforter may possible exceed the weight capacity, it would not be advisable to put it into the washer 'cause you risk destroying your washer!
So in answer to your question, Yes, it is big enough, but I say that while issuing you the above caveat on the weight! Proceed with caution...IFV