How do I get the width of a custom control from within its own class?

I’m creating a custom RangeSlider with a track, an overlapping range and two thumbs to change the range. In XAML I am able to get the width property of the custom RangeSlider by reference binding. In my own case, the label text attribute outputs 352 which is the width of the RangeSlider. I want to use this width to perform calculations, mainly to determine the width of the range and the position of both thumbs at the endpoints of this range.

<Label Text="{Binding Source={x:Reference RangeSlider}, Path=Width}"/>
<controls:RangeSlider x:Name="RangeSlider"/>

How do I get this width property from within the code behind, from the actual RangeSlider controls class itself, for example to calculate the width of the range element?

public class RangeSlider : ContentView {

    private Border Track = new Border
    {
        BackgroundColor = Colors.LightGray,
        StrokeThickness = 0,
        HeightRequest = 2,
        ZIndex = 1
    };

    private Border Range = new Border
    {
        BackgroundColor = Colors.DarkGray,
        StrokeThickness = 0,
        HeightRequest = 2,
        ZIndex = 2
    };

    private Border LeftThumb = new Border
    {
        BackgroundColor = Colors.Black,
        StrokeShape = new Ellipse(),
        StrokeThickness = 0,
        HeightRequest = 12,
        WidthRequest = 12,
        ZIndex = 3
    };

    private Border RightThumb = new Border
    {
        BackgroundColor = Colors.Black,
        StrokeShape = new Ellipse(),
        StrokeThickness = 0,
        HeightRequest = 12,
        WidthRequest = 12,
        ZIndex = 4
    };

    public RangeSlider()
    {
        this.Content = new Grid
        {
            Children =
            {
                Track,
                Range,
                LeftThumb,
                RightThumb
            },
            Padding = new Thickness(16, 3)
        };

        /**
         * My attempts to get the width of this custom control:
         */
        Range.WidthRequest = this.Width;
        Range.WidthRequest = this.Content.Width;
    }
}

Or if applicable, is there a better way to calculate the positions?