  We derive the cutoff length scale of the quadratic gravity in $d \geq 5$
dimensional spacetime by demanding that the quantum focusing conjecture for the
smeared quantum expansion holds at the classical level. The cutoff scale has
different dependence on the spacetime dimension depending on the sign of the
coupling constant of the quadratic gravity. We also investigate a concrete
example of the 5-dimensional Schwarzschild spacetime and directly confirm that
the quantum focusing conjecture holds when the quantum expansion is smeared
over the scale larger than our cutoff scale.
