A very short question.
I'm writing a trilogy. Book 1 was 88,000 words, but book 2 is probably only going to be 75,000 words. That's over 10,000 words less.
Should I find a way to make it longer?
Is there anything to gain by making each book in a series a similar length?
Is 70-75,000 words okay for length? Too short compared to the first?
Make it as long as the story demands - worst case scenario is if it's too big, it can be split into parts (e.g. A Song of Ice and Fire).
There are numerous examples of series with varying book length.
Raymond E Feists Riftwar is a good start - Magician is a substantial book by itself, the following two (Silverthorn and A Darkness at Sethanon) noticeably less.
Wiki puts the page count for that trilogy as follows:
Magician: 545
Silverthorn: 352
Darkness at Sethanon: 425
Plus there are the likes of Harry Potter or Obernewtyn etc where the first books are smaller then the following ones.
There is no 'rule', nor anything to really be gained, by making your books match each other in length. The length should be determined by the story.
No, it doesn't have to be.
Your example: 88k vs 75k. Those are already very similar word-counts. A reader will most likely not tell the difference when reading them.
My example: Alternate history / Historical Fiction. Part 1 will just be the intro that summarizes real history up to the point where alternate history begins. Part 1 exists to ground the story in context and familiarize my audience with a particular nation's culture (and history!) so that future decisions and plot will make sense.
Anyway, Part 1 will probably be 10k words or less which will prolly be 3 times shorter than any other Parts, maybe even 5 times or more. But it makes sense to divide the Parts this way and there is no way you would force yourself to extend the intro just for the sake of matching a future Part, which is prolly a more plot-filled Part.
(10k words is still a pretty long "intro" ofc.) But in my case it will work because the intro is sort of like a story all its own taking a relatively straight ascent to the climax where a major character gets shot. Then Part 2 begins.
Artistically, each book should be as long as it needs to be.
Commercially, there are certain limits determined by salability and risk. A thin book may not be perceived by the reader as value for money and so may not sell. A fat book costs more to produce and so represents a bigger risk for the publisher. So publishers generally want books to fall between the Scylla of unsalability and the Charybdis of risk. Exactly where that is for new authors in a particular genre at any given time is something you probably need to research with an agent of publisher.
However, the range between unsalable and too risky changes greatly if you already have a successful book. If you prove you have an audience willing to snap up a few hundred thousand copies, then both salability and risk issue are substantially reduced and you have a wider range of length to play with. So the answer to you question about your second book really comes down to how well your first book sells.
Similar is a loose word, and you should treat it as such. Your second part is 85% of the first, and that's more than adequately similar. If the size difference is more than half/double then it's a reason to worry and reconsider the structure.
This can be done by expanding, moving either the "cut point" or transferring chapters between the two parts. Or potentially adding a bonus; a separate novelette with cameos of the main story, taking at a different time, included as an extra to the short part. Or just merging the two into a single volume.
Yeah, considering Mikhail Bulgakov's "Theatrical Novel"'s Part II is about 15 pages long, it would make absolutely no sense splitting it off into a separate volume. But if the size difference is of order of order of 70%, there is absolutely nothing to worry.
"Similar", I'd say yes. But they don't have to be identical. I'd say 75,000 and 88,000 are in the same ballpark. If volume 1 was 80,000 words and volume 2 was 5,000 words you should think twice about that. That would almost surely be a totally different type of story. But 75,000 vs 88,000 ... no big deal.
