Dim pMxDoc As IMxDocument
Set pMxDoc = ThisDocument
Dim pMap As IMap
Set pMap = pMxDoc.FocusMap
Dim pSR As ISpatialReference
Set pSR = pMap.SpatialReference
Dim pCurve As ICurve
Set pCurve = [Shape]
pCurve.Project pSR
Output = pCurve.Length