Using Width to constrain the size of elements
<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"> <StackPanel> <Label Width="100">Username</Label> <TextBox Width="150">username@example.com</TextBox> <Label Width="100">Password</Label> <PasswordBox Width="150"></PasswordBox> <Button Width="100" Content="Submit" /> </StackPanel> </Page>