Measured (lordy, I’m turning in to a saddo) with some digital calipers
Rubber Queen 2.4 = 2.39″
Rubber Queen 2.2 = 2.22″
Race King 2.2 = 2.2″
Mountain King 2.4 = 2.40″
They were measured to the widest part of the tyre. On the MK this is the shoulder knob. On the RQ and RK this is the tyre carcass.
FYI the carcass on the MK 2.4″ is approx 2.2″. i.e. the RK 2.2″ is the same volume as the 2.2″ RQ and 2.4″ MK, though all stated sizes were accurate.
HTH
/edit
the rims they were installed on (either Stans 355 or Bonty Rhythm Pro) made naff all difference to the actual widest point, though they did change the shape of the profile.