How can one get the size of a selected subPath without breaking apart?

Simply try:

Sub Test()

Dim OriUnit As Long

OriUnit = ActiveDocument.Unit
ActiveDocument.Unit = cdrInch

' ....

ActiveDocument.Unit = OriUnit

End Sub

Thanks, NudeFan, didn't think about mm conversion. Got it. How can I reduce the number of decimal places to three?

msgbox Format(w, "0.000")

or: MsgBox "Width = " + Format(W, "0.000")

Thanks all, this is where I'm leaving it

Sub SubPathSize()
Dim OS As Shape, x#, y#, w#, h#
Dim OriUnit As Long
OriUnit = ActiveDocument.Unit
ActiveDocument.Unit = cdrInch
Set OS = ActiveSelection.Shapes(1)
For i = 1 To OS.Curve.Segments.Count
If OS.Curve.Segments(i).Selected = True Then
OS.Curve.Segments(i).GetBoundingBox x, y, w, h
MsgBox ("Width = " + Format(w, "0.000") & vbCr & "Height = " + Format(h, "0.000") & vbCr)
End If
Next i
ActiveDocument.Unit = OriUnit
End Sub

How to only show me the greatest number of all of them.
Let's use a combined sponge clipart for example. If I need to know the size of one of the "holes" I can use the smart fill tool and fill that hole and then see the size then delete that. Another method would be to break the whole mess apart. Not good either.
This macro allows one to marquee select the nodes of a "hole" then right click and run the macro. It loops thru and shows several heights and widths but I only need to see the greatest h & w.

Don't know, if I got your problem correct, maybe this will help:

Sub Test01()

Dim CurSh As Shape, SubSh As Shape, i As Integer, MaxS As Double, MaxP As Integer
Dim MyCrv As Curve, MyPath As SubPath

Set CurSh = ActiveShape

For i = 2 To CurSh.Curve.SubPaths.Count
   If i = 2 Then
      MaxS = CurSh.Curve.SubPaths(i).Area
      MaxP = i
   Else
      If CurSh.Curve.SubPaths(i).Area > MaxS Then
         MaxS = CurSh.Curve.SubPaths(i).Area
         MaxP = i
      End If
   End If
Next i

Set MyCrv = ActiveDocument.CreateCurve
MyCrv.AppendCurve CurSh.Curve.SubPaths(MaxP).GetCopy
Set SubSh = ActiveLayer.CreateCurve(MyCrv)
SubSh.Fill.ApplyUniformFill CreateRGBColor(255, 0, 0)
MsgBox "My Size is " + Format(MaxS, "0.000")
SubSh.Delete
CurSh.Selected = True

End Sub