Roughly 65,000 to 100,000 words, and unusually for a subgenre, that range comes from real published sources rather than folklore.
The Mystery Writers of America define the floor as part of an award's eligibility rules, and a major publisher of the genre states its own expectation. That is better evidence than fantasy or thriller can offer.
The Floor: 65,000 Words
The Mystery Writers of America's Lilian Jackson Braun Award exists specifically for cosy mysteries, and its eligibility rules put a number on the form:
"A $2000 prize will be awarded annually for the best full-length, contemporary cozy mystery... To be considered for the award, submissions must meet the following criteria: The book must be a full-length (65K words or more) novel (hardcover, paperback original, or e-book original) first published by an MWA-approved publisher during the calendar year prior to the award being presented."
A professional writers' organisation defining "full-length contemporary cozy mystery" numerically. It is the single best source in this territory, and worth more than any number of blog ranges.
Note what it is: an award eligibility floor, not a target. A 62,000 word cosy is a perfectly good book that is not eligible for this particular prize.
The Working Range: 75,000 to 100,000
Kensington Books, a significant publisher of the genre, states an expectation on its submissions page. From Editor-in-Chief John Scognamiglio's entry, listing "cozy and historical mysteries" among the genres he acquires:
"Word count for mysteries is 75,000-100,000 words."
Joffe Books, whose stated genres include "cosy crime", sets a lower gate: "Your full-length book (minimum 60,000 word count)".
So the sourced picture is a floor somewhere between 60,000 and 65,000, and a working band up to 100,000.
Note that Kensington's figure is attached to mysteries generally rather than cosies specifically, so it covers the wider category. Do not stretch it to cover thrillers, which that editor also acquires but which the sentence does not name.
Where This Sits
Cosy mysteries run shorter than most crime fiction, and the sourced numbers bear that out. The genre's conventions explain why: a contained setting, an amateur detective, violence off the page, and a puzzle that resolves. That structure does not require the length that a police procedural or a psychological thriller often does.
For series, which is how most cosies are published, consistency across books matters more than any individual figure. Readers arrive with an expectation set by book one.
A practical caution about print. At the low end, length interacts with production. A 65,000 word novel at 6 by 9 inches produces a relatively thin book, and below about 80 printed pages KDP prints no spine text at all. A smaller trim size raises the page count and fixes both. See how to choose a trim size for a novel.
What Is Not Sourced
The tighter ranges you will see quoted, typically 70,000 to 80,000 presented as the cosy standard, do not come from any publisher, agency or professional body I could find. They may well describe the market accurately. They are not statements anyone has made.
Malice Domestic, which runs the Agatha Awards and would be the natural second source, is no longer reachable.
What Deckle Does
The word count in Compile is the manuscript figure that a submission or an award entry asks for.
For a series, which is the normal shape of cosy publishing, templates let you carry a structure across books, and comparing final word counts between books in a series is a quick check on whether you are delivering what readers of book one expect.
If a draft lands under a floor you need to clear, the honest fix is a subplot or a scene that earns its place rather than padding. If it lands over, see how to cut word count.
Common Mistakes
- Treating 65,000 as a target. It is an award eligibility floor, not a goal.
- Applying Kensington's figure to thrillers. The sentence names mysteries.
- Quoting a 70,000 to 80,000 range as standard. No source states it.
- Ignoring the print consequence at the low end. A short cosy can produce a spine too thin to carry a title.
- Varying wildly across a series. Readers set expectations from the first book.
FAQ
Q: How long should a cosy mystery be? A: Roughly 65,000 to 100,000 words. The floor comes from the Mystery Writers of America; the upper figure from Kensington.
Q: Is 65,000 words a rule? A: It is the eligibility floor for the MWA's cosy mystery award, not a publishing requirement.
Q: Can a cosy be shorter? A: Yes, though below 40,000 words it is a novella by the standard definition.
Q: Do cosies run shorter than other crime fiction? A: The sourced figures suggest so, and the genre's contained structure supports it.
Q: Should books in a series match in length? A: Roughly. Readers form expectations from the first one.