I know the rule of thumb when I got in the biz was roughly 1 FT person for every 1,000 circulation (at least at the smaller papers).
I worked at two shops:
6,600 circ = 5 FT in newsroom (EIC, Assistant Editor, SE, 2 reporters -- one of which was 3/4 sports). All had bylines
10-11,000 circ = Generally 12 FT, although it has fluctuated (EIC, ME, 2 copy editors, 4 news reporters, 1 photog, 2 FTs in sports, editorial assistant). They've added three positions to work on some new mass-circulation weekly products, so now the newsroom has 16 people (EIC, ME, weekly editor, 3 copy editors, 3 daily reporters, 1 photog, 2 in sports, 2 reporters for weeklies, editorial assistant, one more reporter who splits between weekly news-side and daily sports ... however, though the newsroom has grown, the daily staff has actually lost people -- 2.5 reporters, the community editor and 1 copy editor are promised to the weekly).