j'ai trouvé ceci qui marche
Private Sub Worksheet_Change(ByVal Target As Range)
If Not Intersect(Target, Range("E5:F5")) Is Nothing Then
Application.EnableEvents = False
Dim cell As Range
For Each cell In Intersect(Target, Range("E5:F5"))
If IsNumeric(cell.Value) Then
cell.Value = cell.Value * 1000
cell.NumberFormat = "0.000"
End If
Next cell
Application.EnableEvents = True
End If
End Sub