How to sum gridview column values dynamically in vb.net?

Protected Sub GridView1_DataBound(ByVal sender As Object, ByVal e As System.EventArgs) Handles GridView1.DataBound

        Dim Volume As Decimal = 0

        For Each r As GridViewRow In GridView1.Rows

            If r.RowType = DataControlRowType.DataRow Then

                Volume += Convert.ToDecimal(r.Cells(1).Text)

            End If

        Next

        total1.Text = Math.Round(Volume, 0).ToString()

    End Sub