CW's guideline limit is 10k but I suspect
101 Ways to Leave Paris by Simon Avery in CW10 was around 15 k.
Ellery Queen's Mystery Magazine and Alfred Hitchcock's Mystery Magazine are the world's longest-running short-story mystery magazines.. AHMM prefers
Quote:
that stories not be longer than 12,000 words, EQMM uses stories of almost every length. 2,500-8,000 words is the preferred range, but we occasionally use stories of up to 12,000 words and we feature one or two short novels (up to 20,000 words) each year, although these spaces are usually reserved for established writers.
It won't be easy.