In S3D there are many things that can change your wall thinkness.

You set your Nozzle diameter which is used in calculations, you set your Extrude width which is the thickness you want the extrusion to be. rule of thumb is 1.2x nozzle size. I like .5 for .5 nozzle with my printer. Then other settings that do other things will screw that up.. If the starting height is too low it can cause the wall to be fatter. If the extrusion multiplier is too low walls will be under sized, to high then they are too fat. If the filament diameter setting is set to 1.75 but the filament is actually 1.69 or 1.71 then your expected extrusion will be under extruded and wall too thin. Not sure how cura works but they both do the same thing.. change stl to gcode.. Good luck!