Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As Range)
Dim TaillePoliceNormale%
TaillePoliceNormale = 11 'à adapter
Set Target = Intersect(Target, Sh.UsedRange)
If Target Is Nothing Then Exit Sub
For Each Target In Target 'si entrées multiples (copier-coller)
Target.Font.Size = TaillePoliceNormale - IIf(Len(Target) > 50, 3, 0)
Next
End Sub