How many povs and words per chapter in a mystery novel (the story has 6 povs)?

This is one of those “if you are asking” questions. You see, authors that have a lot of experience working with POV don’t need to ask this question. They know it’s not a matter of how many, but of how well you handle POV for the reader. And multiple POVs are a big problem for the reader. There are a few things that sort of work - I’ll give you an example of one I worked on as an editor. The story had 3 main characters, two of which were given in 1st person and the third in a sort of “chorus” (the meaning from classical theatre) third person. The two main characters were destined to meet eventually, but for the first half of the book, they were in entirely different regions of the world, they were of very different social, economic and educational backgrounds, and had very different day-to-day goals. The story opened with one of the main characters trying to find where, in the formal gardens, his alcoholic mother had hidden her cache of booze while the other main character was trying to get enough to eat and find somewhere safe to sleep the night. The “chorus” character was written as if a historian was writing about the events leading up to the events of the story - which was at times a little confusing but after about 5 chapters, you could get used to it.

The big benefit for the reader of this was that there was never a big “wait who are we with now?” moment at the start of a chapter. The author only needed a couple of sentences and it was obvious who we were with. By the time it got to the point where it was necessary to switch POV mid chapter, the characters had had plenty of time to get established for the reader, so there was no issue knowing who is who.

And that’s the most likely thing to get your book thrown at the wall. Not knowing who is who. I see authors putting the name of the “pov character” at the start of the chapter so the reader “knows” who it is.

Those scare quotes around “knows” are very much the point. One of the challenges for every author in every conventionally written story is to ensure the reader can remember who the characters are, and put names to them. Mystery writers who want a large pool of suspects have to spend a lot of time working and reworking so that the reader knows who the hell they are talking about. If you caught Ken Branagh’s Orient Express movie (2017) you will notice it’s packed full of big name stars. That’s the moviemaker’s technique to ensure you quickly remember who is who. That’s literally the reason for it. The 1974 version uses exactly the same technique.

The challenge of how to do the same in a novel is one that Agatha Christie (who wrote the book “Murder on the Orient Express”) struggled with at times, but for which she developed a wide range of techniques.

And this is without POV.

Once you start using multiple POV you have to ensure you solve this problem, and labelling chapters with the character name only works for the author.

If you’re writing in 3rd person, using carefully controlled psychic distance to manage character point-of-view, you can at least refer to the character by name a couple of times in the first paragraph, and maybe refer to something characteristic about them.

If you’re writing in 1st person, you have to have an answer to the question “how can I be sure the reader knows immediately and instinctively which character this is,” whenever you switch to them.

With 6 POVs, the name of the character is never going to be enough. Tying the character to a location in time and space, to a milieu, to an attitude, a style of action, a register of speech - all of these will help a great deal. But NOTHING will make it easy.

Look: the only way an artist acquires a difficult skill is by ignoring wiser voices who tell them not to try. The only way you can become skilful at dealing with many POVs (and anything more than 2 is many), is by trying to do it. So what I’m trying to do is make you aware of what is going to go wrong, so you can be actively looking for solutions that work for you. The number of authors who succeed in writing a good, cohesive narrative that involves narration via 6 different POVs can be counted on the fingers of one head. Doing this is always going to sacrifice other features of a satisfying story that most readers view as a hard requirement. But if you have the motivation and ambition to ignore the wiser voices, you can find ways to make this work. I’ve seen it done.