Hi Mark,
I have been experimenting with the Sketchup import "options" button and found that for example a drawing produced in AutoCAD using inches as the units of measurement must be imported into Sketchup using the same measurement option. If the import units are inadvertedntly set to feet then all dimensions will appear in Sketchup x 12. Setting the import dimensions to match those used in the originating problem should solve your problem.
Regards
Ken Hume