CAD tip # 13963:

Run the macro in the assembly environment, not in an open Pipe, Pipe run or Route.

'Add lengths of all pipes (CADforum.cz)
Dim docFile As Document
Dim customPropSet As PropertySet
Dim oDocInts As DocumentInterests
Dim bHas_TP_Interest As Boolean 
Dim TotalL As Double
Dim uom = ThisDoc.Document.UnitsOfMeasure

TotalL = 0
For Each docFile In ThisApplication.ActiveEditDocument.AllReferencedDocuments
	customPropSet = docFile.PropertySets.Item("Inventor User Defined Properties")
	oDocInts = docFile.DocumentInterests 
	bHas_TP_Interest = oDocInts.HasInterest("{4D39D5F1-0985-4783-AA5A-FC16C288418C}") 'T&P

	If bHas_TP_Interest Then
		Try
			PL = customPropSet.Item("PL").Value 'string
			PL = uom.GetValueFromExpression(PL, _
					uom.GetStringFromType(UnitsTypeEnum.kDefaultDisplayLengthUnits))
			TotalL = TotalL + PL
		Catch
		End Try
	End If
Next
MsgBox("Total length:" & vbCrLf & vbCrLf & _
		uom.GetStringFromValue(TotalL, UnitsTypeEnum.kDefaultDisplayLengthUnits), _
		MsgBoxStyle.Information, "Pipe lengths")

Another option for obtaining pipe, hose, and tube lengths is the Tube&Pipe assembly BOM - the sum of the Pcs column containing the segment lengths.

You can also get information about the lengths of the segments that make up a pipe assembly by double-clicking on a specific route in the browser tree: