The relative magnitudes of the Grashof number and the square of the Reynolds number determine which form of convection dominates. If G r / R e 2 ≫ ≫ 1 , forced convection may be neglected, whereas if G r / R e 2 ≪ ≪ 1 , natural convection may be neglected. If the ratio, known as the Richardson number, is approximately one, then both forced and natural convection need to be taken into account.