To satisfy your inner API maths hunger (surely that’s a thing?), here is how Revit “thinks” about Length:

Notice the recurring “328083…” theme? This is how it relates:

Check out the comprehensive list of Revit internal units (across all unit types) at:
Revit Units .NET API: Figure Out Revit Internal Units Per Unit Type (pt. 2) – RevitNetAddinWizard & NavisworksNetAddinWizard