/// <summary>
    /// TabControl 
    /// </summary>
    public class DivideValueConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return System.Convert.ToDouble(value) / System.Convert.ToDouble(parameter);
        }

        
 
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

 
<UserControl.Resources>
        <local:DivideValueConverter x:Key="DivideValueConverter" />
    </UserControl.Resources>

xaml:

   <dragablz:TabablzControl >
            <dragablz:TabablzControl.ItemContainerStyle>
                <Style BasedOn="{StaticResource MaterialDesignDragableTabItemStyle}" TargetType="{x:Type dragablz:DragablzItem}">
                    <Style.Triggers>
                        <
 
Trigger Property="IsSelected" Value="True">
                            <Setter Property="themes:MaterialDesignAssist.IndicatorBrush" Value="LightGoldenrodYellow" />
                        </Trigger>
                    </Style.Triggers>
                    <Setter Property="Width" Value="{Binding ActualWidth, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type dragablz:TabablzControl}}, Converter={StaticResource DivideValueConverter}, ConverterParameter=8}" />
                </Style>
            </dragablz:TabablzControl.ItemContainerStyle>
            <dragablz:TabablzControl.InterTabController>
                <dragablz:InterTabController />
            </dragablz:TabablzControl.InterTabController>
            <TabItem
              
            </TabItem>
            <TabItem
              
            </TabItem>
        </dragablz:TabablzControl>