I have a wall in 3ds max. Set to metric. 2.56 meters wide and 2.56 meters tall.
Why when I import to unity it’s either ENORMOUS or TINY?!!?!? 
Scale factor is 1 unit = 1 meter in max.
Have you checked the import scale in the fbx import settings? By default it is set to 0.01, which would make your model tiny.
Yes. its either super large or super tiny. How do I fix this so 1 meter in max is a meter in unity…
If you’re using the FBX Exporter in Max, set the units in the exporter to “Centimeters”. Then when importing in Unity make sure the scale is set to “1” and not “0.01”.