Sub Demo()
Dim lRow As Long, i As Long, j As Long, k As Long, StrTmp As String, StrOut As String
With ActiveSheet.UsedRange
  'Loop through each cell in column C
  For i = 3 To .Cells.SpecialCells(xlCellTypeLastCell).Row
    With .Cells(i, 3)
      StrOut = ""
      'Split the cell results by spaces for parsing
      k = UBound(Split(.Text, " "))
      'Process each 'word'
      For j = 0 To k
        StrTmp = Split(.Text, " ")(j)
        'See what the 'word' ends with
        Select Case Right(StrTmp, 1)
          'If it ends with ', try a ft:m conversion
          Case "'"
            StrTmp = Split(StrTmp, "'")(0)
            If IsNumeric(StrTmp) Then
              StrOut = StrOut & " " & Format(StrTmp * 0.3048, "0.00") & "m" & " (" & StrTmp & "')"
            Else
              StrOut = StrOut & " " & StrTmp
            End If
          'If it ends with ", try a in:cm conversion
          Case """"
            StrTmp = Split(StrTmp, """")(0)
            If IsNumeric(StrTmp) Then
              StrOut = StrOut & " " & Format(StrTmp * 2.54, "0.00") & "cm" & " (" & StrTmp & """)"
            'If it ends with " and contains ', try a ft&in:cm conversion
            ElseIf InStr(StrTmp, "'") > 0 Then
              If IsNumeric(Split(StrTmp, "'")(0)) And IsNumeric(Split(StrTmp, "'")(1)) Then
                StrOut = StrOut & " " & Format(Split(StrTmp, "'")(0) * 0.3048 + Split(StrTmp, "'")(1) * 2.54, "0.00") & "cm" & " (" & StrTmp & """)"
              Else
                StrOut = StrOut & " " & StrTmp
              End If
            Else
              StrOut = StrOut & " " & StrTmp
            End If
          Case Else
            'If it's not ft/in, look for other possibilities
            If IsNumeric(StrTmp) And j < k Then
              'If the next 'word' is GPM, do a GPM:CMH conversion
              If Split(.Text, " ")(j + 1) = "GPM" Then
                StrOut = StrOut & " " & Format(StrTmp / 1000 * 3.78544 * 60, "0.00") & " CMH" & " (" & StrTmp & " GPM)"
                j = j + 1
              Else
                StrOut = StrOut & " " & StrTmp
              End If
            Else
              StrOut = StrOut & " " & StrTmp
            End If
        End Select
      Next
        .Value = StrOut
    End With
  Next
End With
End Sub