Staffing ratios in public libraries

To those of you who work or have worked in public libraries: what is your ideal per-location ratio of staff to patrons (as measured by, say, quarterly gate count—although I’m not at all sure that’s the best metric)? How many staff are needed at a given library that sees 10,000 visits per quarter, vs. one that sees 35,000 per quarter?

… I imagine this will vary by community, but I also imagine there will be some overlap. Interested to hear opinions!