Моя кнопка находится в сетке Grid. Когда я задаю MinWidth определяется минимальная ширина для содержимого кнопки (Content)
<Window x:Class="Encryption.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:Encryption"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="63*" />
<RowDefinition Height="31*" />
<RowDefinition Height="46*" />
<RowDefinition Height="47*" />
<RowDefinition Height="46*" />
<RowDefinition Height="47*" />
<RowDefinition Height="47*" />
<RowDefinition Height="46*" />
<RowDefinition Height="46*" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="88*" />
<ColumnDefinition Width="61*" />
<ColumnDefinition Width="115*" />
<ColumnDefinition Width="88*" />
<ColumnDefinition Width="88*" />
<ColumnDefinition Width="88*" />
<ColumnDefinition Width="88*" />
<ColumnDefinition Width="61*" />
<ColumnDefinition Width="115*" />
</Grid.ColumnDefinitions>
<TextBox HorizontalContentAlignment="Center" VerticalContentAlignment="Center" TextWrapping="Wrap" RenderTransformOrigin="0.5,0.5" Background="White" x:Name="InputText" Grid.Column="3" Grid.ColumnSpan="3" Grid.Row="1"/>
<Button Content="Зашифровать" FontSize="15" x:Name="EncryptionButton" Click="EncryptionButton_Click" Grid.ColumnSpan="3" Grid.Column="3" Grid.Row="3"/>
<ComboBox HorizontalContentAlignment="Center" VerticalContentAlignment="Center" Grid.Row="1" MinWidth="61" Grid.Column="1">
<Label Content="C"/>
<Label Content="D"/>
<Label Content="E"/>
<Label Content="F"/>
<Label Content="G"/>
</ComboBox>
<Label Content="" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" Margin="0,1,0,0" FontSize="25" x:Name="Result" Grid.ColumnSpan="7" Grid.Row="5" Background="White" Grid.Column="1"/>
</Grid>
</Window>
