This paper reports the relationship between the length of panel side and the deflection of the sandwich panels with corrugated core. The deflections of the sandwich panels having the lengths of panel side from 100 to 1300 mm and the height of the panel of 13.6 mm were determined by finite element method, where the four sides of the panel were rigidly fixed and a uniformly distributed load was applied to the top surface of the panel. The maximum deflection at the center of the panel increases with increasing the length of panel side, confirming that a power law is established between the length of panel side and the deflection. The scaling exponent of the sandwich panel was about 3.3 and this value was smaller than that of the single plate, i.e., 4. The ratio of the weight of the sandwich panel to that of the single plate having the same length of the panel side and the different thickness, which becomes same deflection compared to the sandwich panel, was found to be smaller as the length of the panel side becomes longer. This effect of weight reduction was possible to be estimated analytically. Smaller value of scaling exponent of the sandwich panel compared to that of single plate was found be related with that the normal force applied to the panel was effectively converted to the shear force at the bonding interface between the core and the bottom plate.