Our building has 2 per key per department. Each key also has a flex om where they have a home department, but know all departments so they can fill in for vaca and whatnot.Depends on building type, head count and volume. Typically it's two per department per shift. It can range from 1.5 to 2. The .5 being a mid who works part of 2 shifts. So an a-key mid or a b-key mid.
But things happenn promotions, exec turnover etc which can impact the number. If the OM is the exec trainer for the department you may have a couple of trainees or an intern or two.
Or sometimes if a shift is struggling they may send a more experienced OM to get another set of eyes and try and figure out what the gaps are, so you may have 3.