I retopologized my high res mesh in Zbrush. I exported the low res mesh as obj file but I never put it inside another 3d application like 3ds Max or Maya. When I appended the low res mesh into my high res mesh subtool, I saw that the low res mesh became really small, almost as small as the toes of the high res mesh. How is this possible??? When I was retopologizing the high res mesh, I did NOT even mess around with the scale. Help 
Not sure but check if in Tool>Export your scale is set diferent to 1.
I tried it, didn’t work
you can click “unify” in the deformation palette for both of them. that should make them the same size.