You can use a user-defined CentimetersToPoints function:
Code:
Function CentimetersToPoints(Cm As Single)
CentimetersToPoints = Cm * 28.3464566929134
End Function
which you might call like:
Code:
Sub Demo()
Dim cht As ChartObject
Set cht = ActiveSheet.ChartObjects.Add(Left:=CentimetersToPoints(3), Top:=CentimetersToPoints(4), Width:=CentimetersToPoints(6), Height:=CentimetersToPoints(5))
End Sub