story lengths

I've been asked how many words make up a short story or a novel, and what is the difference - in terms of length - between a novella and a novelette.

For peace of mind, I use the word counts used by the Science Fiction Writers of America (SFWA):

Vignette - under 1,000 words
Short Story - 1,000 - 7,499 words
Novelette - 7,500 - 17,4999 words
Novella - 17,500 - 39,999 words
Novel - 40,000 words

Personally, my short fiction usually falls in the 3500 - 6000 words range. I don't plan the length ahead of time but my stories usually end when they want to end, way before 7,499 words.

I'm very uncomfortable with novelette and novella length (though maybe I can write a novelette). My thought process is "might as well go for full-length novel while I'm at it."