Use the AutoSize, FixedCellHeight and FixedCellWidth properties to defines the size of the control's cell. A cell displays a date. The FixedCellHeight and FixedCellWidth properties has effect only if the AutoSize is False. By default, the AutoSize property is True. The following sample fixes the cell's size to (18,32): 

Private Sub Form_Load()
    With CalendarCombo1
        .AutoSize = False
        .FixedCellHeight = 18
        .FixedCellWidth = 32
    End With
End Sub