I think that there are two aspects of ‘how long should a novel be’? There is the author’s perspective and the industry perspective.

I think I’m a little bit familiar with both.

As author, I have sold a few short stories and have a few weeks ago started marketing my first novel (yay). I’m one of those people who looks at an idea and goes – hmmm – this is 120K story. I don’t know how I do that – I just do. Over the past year or so, I have listened to and read advice from many in the fiction industry telling me that a first time author should submit something no longer than 120K (on the pain of death). I tend to be a tad skeptical about that. A little while ago, we got a few friends together and estimated the length of first books recently published. It was more like 130-140K. I think the message here is that if you haven’t published a novel, the industry will push you towards shorter submissions, but they will take longer ones if they like it, but if you have a 180K beast, it’s going to be a much harder sell, unless you cut it down, which, as you say, may not be all that hard.

From the industry perspective, I have written and published books in non-fiction. Buyers expect a certain length, size, quality, value-for-money, and in my case (shudder) full colour. I suspect that fantasy books are bigger simply because readers expect them to be and publishers are listening to this. The need for explanation also holds for Science Fiction, yet those books are often much thinner, so I’m not sure the worldbuilding argument holds. Fantasy just tends to move at a slower pace or encompass greater events. I think the bottom line is that (female) readers want their fantasies to be fat.

Having done typesetting, though, it is really, really amazing what you can do with font choice, margin size and line spacing. So what if SF readers expect their books to be skinny. You can squish 130K into a smallish book.

For an author, especially if you’re unpublished, I think you move into slightly dangerous territory if you go much over 140K.

Does that make sense?