How can I Identify Range And Then Last Cell In Range And Insert Absolute Cell Address Into R1C1 Formula?

• TargetWeight.Address.Row should be TargetWeight.Row
• TargetWeight.Address.Column should be TargetWeight.Column
• When you create an xlR1C1 style address, the n inside [n] is a relative row or column adjustment. RC[-1] means same row, one column left. You want an absolute address and you have absolute row and column as long integers so R" & totalweightr & "C" & totalweightc

• You don't Set integer values, you assign them with an =. You only Set objects like ranges, cells, worksheets, etc.

  For Each cell In rng2
      If cell.Offset(0, -1).Value <> "" Then
          Set sidewight = cell.Offset(0, -1)
          Set TargetWeight = sideweight.End(xlDown)
          TargetWeightr = TargetWeight.Row
          TargetWeightc = TargetWeight.Column
          cell.FormulaR1C1 = "=RC[-1]/R" & TargetWeightr & "C" & TargetWeightc
      End If
  Next cell
  

You might also want to forget all of the manipulation and just use TargetWeight.Address in xlR1C1 style.

For Each cell In rng2
    If cell.Offset(0, -1).Value <> "" Then
        Set sideweight = cell.Offset(0, -1)
        Set TargetWeight = sideweight.End(xlDown)
        cell.FormulaR1C1 = "=RC[-1]/" & TargetWeight.Address(referencestyle:=xlR1C1)
    End If
Next cell