You need to export to STL in millimeters, i.e. I am working in centimeter in 3ds max and when exporting something like 10x10x20cm model without changing it's scaling, I would end up with 1x1x2cm 3D print, so I need to scale the model to 1000% in order to get the proper 10x10x20cm 3D print STL format.
In other words, it does not matter in what units you are working in your 3D modeling software as they will be interpreted as millimeters by 3D printing software (5in will be 5mm in 3D print, 0,2 meters will be 0,2mm, etc.).