answer:It’s actually variable. While most AC electric motors in the US spin at either 1700–1800 or 3500–3600 RPM because of our 60Hz electrical system, those beaters are not driven directly; there is a drivetrain involved that gears it down, and what the exact gear ratio is is not the same in every vacuum. If I had to guess though, based on how fast I can wrap an unseen cat toy around the roller on mine, I’d say 600 RPM (10 revs a second) tops, at least on mine.