WPF Grid is not stretching vertically

Question

I've the following Grid in the main window:

<Grid Name="gridMain" Width="Auto" VerticalAlignment="Stretch" Height="Auto">
</Grid>

I'm adding a UserControl dynamically in the grid. The main window only has this grid. I want the grid to be stretched both horizontally and vertically and should fill up entire window. The grid is stretching horizontally but doesn't stretch vertically. Any idea why? What do I need to do to make the grid stretch vertically?

EDIT

Here is the complete XAML.

<Window x:Class="Sensitech.TurboValidator.UserControls.ConveyorBelt"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="ConveyorBelt" Height="329" Width="714" xmlns:my="clr-namespace:System.Windows.Controls.DataVisualization.Charting;assembly=System.Windows.Controls.DataVisualization.Toolkit">
    <Grid Name="gridMain" Width="Auto" VerticalAlignment="Stretch" Height="Auto" Background="Cyan">

    </Grid>
</Window>

Answer 1

Try setting row height to *

<Grid Name="gridMain" >    
    <Grid.RowDefinitions>
        <RowDefinition Height="*"/>
    </Grid.RowDefinitions>
</Grid>

Similarly define ColumnDefinition and set Width to *

Also make sure grid is the one not stretching not the user control. You can easily do that by assigning some background color to Grid.