It's the same piece of furniture. Here in the USA we commonly use both words. I've heard sofas and couches called Chesterfields in some parts of the world but you wouldn't want to use that word here in America. That's an antiquated term for a sofa. Only a handful of people would know what you mean if you use Chesterfield. And everyone else would think you want a cigarette because that's the brand name of a cigarette.

They're exactly the same thing. 'Sofa' is more common in British English and 'couch' is more common in American English, but any native speaker would understand you whichever word you used. The word 'couch' makes me think of a 'psychiatrist's couch'. By the way, don't say 'Chesterfield' in Britain, because nobody would understand that here, either. It's the name of a city, not a piece of furniture. When I googled the word, all the sites were American.

As all the other answers point out, they are the same thing. In Britain, we mainly use sofa.

The words mean the same which is basically a long seat covered with fabric for two or more people. Most people use couch when speaking. Example: Have a seat on the couch. Or I left the book on the couch. Sofa is not used as much in every day conversation. Oftentimes the word sofa is used by furniture stores when they are selling couches (don't know why) and most people know that sofa is the same as a couch. The more common word for you to use would be couch. Hope this helps

To tell you the truth there is no difference. We use it interchangeably in the US. however, I think we use sofa more often. I think "couch" came from the French into English years ago meaning "to lie down".