Angular frequency is measured in *radians per second*. In one cycle, (a full revolution) we have 2pi radians. If the pendulum completes 3 cycles in 12 seconds, it averages 1 cycle every 4 seconds, or 1/4 cycles per second (we call cycles per second *Hertz*, abbreviated Hz).
Converting to radians, we find an angular frequency of 1/4 * 2pi = pi/2 radians per second
