Different prefabs having same scale have different size

I downloaded some objects from Google Poly, I can see that their scale is defined as (1,1,1). But when I drag and drop some objects in my scene I see that although their scales are same, they have huge size difference. I want a ‘global’ relative to ground scale reference. How can I do it? I want to resize all the objects so that they are relatively of nearly the same size.

Click on the model object in the project panel then in the inspector panel check if the scale factor is equivalent to the other models (If they have the same size in the scale factor but in the hierarchy they have size difference then it means that the models scale has been changed in the 3D modelling software prior to importing them to the project.