The moment of inertia for a cylinder of mass 'm' and radius 'r' is I = (m*r^2)/2. The average circumference of an adult head is stated to be 55 cm, yielding a radius of approximately 9 cm. Plugging this figure, along with the stated mass, into the listed equation, we have I = (62.5*0.09^2)/2 = 0.25 kg m^2.
