AutoCAD Civil 3D uses conversion factors if the LandXML file you are importing has different units from the current drawing.
You can import LandXML files that use feet or meters.
When imported, the LandXML files are converted to the units of the current drawing. In AutoCAD Civil 3D, the default drawing units can be meters, International Feet, or U.S. Survey Feet. For more information, see Specifying Units and Zone Settings.