Sometimes, series just happen. You’re toodling along, writing your novel and realize you’ve got more than 100,000 words. Unless you’re a bestselling author, that’s too long for a book. Now you’ve got a decision to make. Slash your word count or start a series?

I suspect outliners don’t have that problem, but we explorers do (my term for pantsers).
Series are good! Unless you’re that guy that points out the problems with series. The first book doesn’t have to be good, it has to be great for readers to want to pick up the second book and that has to be even greater for the third book to be picked up.
Yeah, yeah, yeah, needs must, and all that.
The trick is having enough stories to break it into a series.
My series, Hammer Springs, started as a single book (which became the third book in the four books series, which may now become a five book series.)
The first book was about a tragic love story. The second about racism in a small town, the third about two bored kids who build a hurricane car and use it, the fourth book was a love story, but now it’s too long, so maybe the fourth book is about a mayoral election and grieving, pushing the love story to the fifth book.
Some may say I’m an undisciplined writer, to which I say I’m undisciplined in just about everything… why should this be different? More generous people say I just have too much story in my head. That would be nice, it would explain why I have too little memory retention these days. Any excuse would be nice.
Here’s the thing about a series. You end up loving your characters, more so than in a single novel, because you’re developing them (or they’re developing themselves) for a greater span of their lives. They become real to you.
Funny story. Hammer Springs is a fictional place. I know this. However, when I was trying to figure out where to put GCU and The Colony, after searching about the Gulf coast, I needed to reorient myself to the town, so I map quested Hammer Springs. Oh yeah, it isn’t real.
Another funny story. Hammer Springs was supposed to be Brooksville, FL, which has an ugly racial background. I intended to get over and visit Brooksville, take reference photos and get to know the place. COVID hit, traveling was down, and we moved to the middle of the country. Never got to see Brooksville, so made up Hammer Springs. I highly recommend inventing towns if there are going to be negative casts to your story.
Third funny story. I did research on small town racism in the 40s and 50s. You’d think it would be a homogenous thing, but it wasn’t at all. Some small towns were deadly to Black people, others just segregated, and a few mostly skipped racism altogether. That meant Hammer Springs didn’t have to be a horrible place. Very little physical abuse, mostly segregation and a stick-to-your-place-we’ll-stick-to-ours kinda thing. Doesn’t mean violence doesn’t happen, nor that mental and emotional abuse doesn’t happen, or that racism in any form is intolerable, but I didn’t have to get uglier than I wanted to.
I figure my few dedicated readers will pick them all up. That’s enough. If I did this for money, I’d have died from malnutrition decades ago.
So, what’s too long and what’s too short for a novel? For adult readers, 60 to 80 thousand words are the goal. You can undercut that quite a bit and make it a 20 to 40 thousand word novella. The Stephen King’s of the word can get away with triple digit books, but printing costs get high over 80k, so keep ’em around there. If you go longer, slash or series, your choice.