ActiveReport.NETで文字列の長さを取得するには？

Private Function FontResizer(ByRef opTxtBox As DataDynamics.ActiveReports.TextBox) As System.Drawing.Font

    Const INCH_TO_POINT As Single = 72  '1インチ72ポイントとして計算
    Const FONT_NAME As String = "ＭＳ ゴシック"

    Dim CtrlWidth As Single = opTxtBox.Size.Width * INCH_TO_POINT
    Dim CtrlHeight As Single = opTxtBox.Size.Height * INCH_TO_POINT
    Dim WordLength As Integer = opTxtBox.Text.Trim.Length

    Dim DefCtrlWidth As Single
    Dim DefCtrlHeight As Single
    Dim DefFontSIze As Single
    Dim LineCnt As Integer = 1
    Dim TmpFont As System.Drawing.Font
    Dim TmpFontSize As Single
    Dim DefWordLength As Double

    Do
        DefCtrlWidth = CtrlWidth * LineCnt    'ワードラップした場合の描画幅
        DefCtrlHeight = CtrlHeight / LineCnt    'ワードラップした場合の描画高
        TmpFontSize = DefCtrlWidth / WordLength
        If DefCtrlHeight < TmpFontSize Then
            TmpFontSize = DefCtrlHeight
        End If
        TmpFont = New System.Drawing.Font(FONT_NAME, TmpFontSize, FontStyle.Regular, GraphicsUnit.Point)
        TmpFontSize = TmpFontSize - TmpFont.GetHeight(GraphicsUnit.Point)

        LineCnt += 1

        DefCtrlHeight = CtrlHeight / LineCnt
        DefFontSIze = DefCtrlHeight
        TmpFont = New System.Drawing.Font(FONT_NAME, DefFontSIze, FontStyle.Regular, GraphicsUnit.Point)
        DefFontSIze = DefFontSIze - TmpFont.GetHeight(GraphicsUnit.Point)

        If TmpFontSize > DefFontSIze Then
            TmpFontSize = CType(System.Math.Floor(TmpFontSize), Single)
            Return New System.Drawing.Font(FONT_NAME, TmpFontSize, FontStyle.Regular, GraphicsUnit.Point)
        Else
            DefWordLength = System.Math.Floor(DefCtrlWidth / DefFontSIze)
            If WordLength <= DefWordLength Then
                DefFontSIze = CType(System.Math.Floor(DefFontSIze), Single)
                Return New System.Drawing.Font(FONT_NAME, DefFontSIze, FontStyle.Regular, GraphicsUnit.Point)

            End If
        End If

    Loop

End Function