Writing a short story is different from writing a novel. Just as writing a film is different than writing for television. Both the short story and the novel can be mastered by a writer. But each requires a different process.
"Good short stories are made from the writer's emotions alone...done with small personal experiences...let the imagination play with such incidences as a faintly heard song and an invaded apartment, and see what evolves. Other experiences are quieter...The writer will seize on even the smallest, and turn it use if he can." (Patricia Highsmith, p.16, 22, 24.)
So how long is a short story? According to Book Riot dot com, here is a general range for works of fiction:
The eBooks are available through the links to EBSCOhost and O'Reilly Learning.
Highsmith, P. (2001). Plotting and writing suspense fiction. St Martin's Griffin.