diff --git a/src/Orc.Theming.Example/ViewModels/Tools/FontSizeViewModel.cs b/src/Orc.Theming.Example/ViewModels/Tools/FontSizeViewModel.cs
new file mode 100644
index 0000000..da305b1
--- /dev/null
+++ b/src/Orc.Theming.Example/ViewModels/Tools/FontSizeViewModel.cs
@@ -0,0 +1,8 @@
+namespace Orc.Theming.Example.ViewModels
+{
+    using Catel.MVVM;
+
+    public class FontSizeViewModel : ViewModelBase
+    {
+    }
+}
diff --git a/src/Orc.Theming.Example/Views/ControlPaddingsView.xaml b/src/Orc.Theming.Example/Views/ControlPaddingsView.xaml
index 196e365..828297d 100644
--- a/src/Orc.Theming.Example/Views/ControlPaddingsView.xaml
+++ b/src/Orc.Theming.Example/Views/ControlPaddingsView.xaml
@@ -8,6 +8,7 @@
              xmlns:system="clr-namespace:System;assembly=System.Runtime"
              mc:Ignorable="d" 
              d:DesignHeight="450" d:DesignWidth="800">
+    
     <StackPanel Orientation="Vertical">
         <orccontrols:WatermarkTextBox Watermark="WatermarkTextBox"/>
         <TextBox Text="TextBox"/>
@@ -15,4 +16,5 @@
         <orccontrols:FilterBox Text="FilterBox"/>
         <orccontrols:DateTimePicker Value="{x:Static system:DateTime.Now}"/>
     </StackPanel>
+    
 </catel:UserControl>
diff --git a/src/Orc.Theming.Example/Views/MainWindow.xaml.cs b/src/Orc.Theming.Example/Views/MainWindow.xaml.cs
index 934c343..85cecda 100644
--- a/src/Orc.Theming.Example/Views/MainWindow.xaml.cs
+++ b/src/Orc.Theming.Example/Views/MainWindow.xaml.cs
@@ -25,10 +25,10 @@ private void LoadTabItems()
         });
 
         var viewsToAdd = (from viewType in GetType().Assembly.GetTypesEx()
-            where typeof(UserControl).IsAssignableFromEx(viewType) &&
-                  viewType != typeof(ControlsView)
-            orderby viewType.Name
-            select viewType);
+                          where typeof(UserControl).IsAssignableFromEx(viewType) &&
+                                viewType != typeof(ControlsView)
+                          orderby viewType.Name
+                          select viewType);
 
         foreach (var viewToAdd in viewsToAdd)
         {
diff --git a/src/Orc.Theming.Example/Views/Tools/FontSizeView.xaml b/src/Orc.Theming.Example/Views/Tools/FontSizeView.xaml
new file mode 100644
index 0000000..9450d51
--- /dev/null
+++ b/src/Orc.Theming.Example/Views/Tools/FontSizeView.xaml
@@ -0,0 +1,98 @@
+<catel:UserControl x:Class="Orc.Theming.Example.Views.FontSizeView"
+                   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+                   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                   xmlns:catel="http://schemas.catelproject.com"
+                   xmlns:ribbon="clr-namespace:Orc.Theming.Example"
+                   xmlns:orctheming="http://schemas.wildgums.com/orc/theming"
+                   xmlns:orccontrols="http://schemas.wildgums.com/orc/controls">
+
+    <orccontrols:StackGrid>
+        <Grid.RowDefinitions>
+            <RowDefinition Height="Auto" />
+            <RowDefinition Height="*" />
+        </Grid.RowDefinitions>
+
+        <Grid.ColumnDefinitions>
+            <ColumnDefinition Width="*" />
+            <ColumnDefinition Width="*" />
+        </Grid.ColumnDefinitions>
+
+        <Label Content="Default font size"
+               Grid.ColumnSpan="2" 
+               HorizontalAlignment="Center" />
+
+        <GroupBox Header="No subscriptions">
+            <StackPanel Orientation="Horizontal">
+                <GroupBox Header="Scaling">
+                    <StackPanel Orientation="Vertical"
+                                HorizontalAlignment="Left">
+                        <Label Content="This is 0.6"
+                               FontSize="{orctheming:FontSize Scale=0.6}" />
+                        <Label Content="This is 0.8"
+                               FontSize="{orctheming:FontSize Scale=0.8}" />
+                        <Label Content="This is 1.0"
+                               FontSize="{orctheming:FontSize Scale=1.0}" />
+                        <Label Content="This is 1.2"
+                               FontSize="{orctheming:FontSize Scale=1.2}" />
+                        <Label Content="This is 1.4"
+                               FontSize="{orctheming:FontSize Scale=1.4}" />
+                    </StackPanel>
+                </GroupBox>
+
+                <GroupBox Header="Delta">
+                    <StackPanel Orientation="Vertical"
+                                HorizontalAlignment="Left">
+                        <Label Content="This is -4"
+                               FontSize="{orctheming:FontSize Delta=-4}" />
+                        <Label Content="This is -2"
+                               FontSize="{orctheming:FontSize Delta=-2}" />
+                        <Label Content="This is 0"
+                               FontSize="{orctheming:FontSize Delta=0}" />
+                        <Label Content="This is +2"
+                               FontSize="{orctheming:FontSize Delta=2}" />
+                        <Label Content="This is +4"
+                               FontSize="{orctheming:FontSize Delta=4}" />
+                    </StackPanel>
+                </GroupBox>
+            </StackPanel>
+        </GroupBox>
+
+        <GroupBox Header="Subscriptions">
+            <StackPanel Orientation="Horizontal">
+                <GroupBox Header="Scaling">
+                    <StackPanel Orientation="Vertical"
+                                HorizontalAlignment="Left">
+                        <Label Content="This is 0.6"
+                               FontSize="{orctheming:FontSize Scale=0.6, SubscribeToEvents=True}" />
+                        <Label Content="This is 0.8"
+                               FontSize="{orctheming:FontSize Scale=0.8, SubscribeToEvents=True}" />
+                        <Label Content="This is 1.0"
+                               FontSize="{orctheming:FontSize Scale=1.0, SubscribeToEvents=True}" />
+                        <Label Content="This is 1.2"
+                               FontSize="{orctheming:FontSize Scale=1.2, SubscribeToEvents=True}" />
+                        <Label Content="This is 1.4"
+                               FontSize="{orctheming:FontSize Scale=1.4, SubscribeToEvents=True}" />
+                    </StackPanel>
+                </GroupBox>
+
+                <GroupBox Header="Delta">
+                    <StackPanel Orientation="Vertical"
+                                HorizontalAlignment="Left">
+                        <Label Content="This is -4"
+                               FontSize="{orctheming:FontSize Delta=-4, SubscribeToEvents=True}" />
+                        <Label Content="This is -2"
+                               FontSize="{orctheming:FontSize Delta=-2, SubscribeToEvents=True}" />
+                        <Label Content="This is 0"
+                               FontSize="{orctheming:FontSize Delta=0, SubscribeToEvents=True}" />
+                        <Label Content="This is +2"
+                               FontSize="{orctheming:FontSize Delta=2, SubscribeToEvents=True}" />
+                        <Label Content="This is +4"
+                               FontSize="{orctheming:FontSize Delta=4, SubscribeToEvents=True}" />
+                    </StackPanel>
+                </GroupBox>
+            </StackPanel>
+        </GroupBox>
+
+    </orccontrols:StackGrid>
+
+</catel:UserControl>
diff --git a/src/Orc.Theming.Example/Views/Tools/FontSizeView.xaml.cs b/src/Orc.Theming.Example/Views/Tools/FontSizeView.xaml.cs
new file mode 100644
index 0000000..67f04f4
--- /dev/null
+++ b/src/Orc.Theming.Example/Views/Tools/FontSizeView.xaml.cs
@@ -0,0 +1,9 @@
+namespace Orc.Theming.Example.Views;
+
+public partial class FontSizeView
+{
+    public FontSizeView()
+    {
+        InitializeComponent();
+    }
+}
diff --git a/src/Orc.Theming.Tests/PublicApiFacts.Orc_Theming_HasNoBreakingChanges_Async.verified.txt b/src/Orc.Theming.Tests/PublicApiFacts.Orc_Theming_HasNoBreakingChanges_Async.verified.txt
index b848b0d..09f3bc0 100644
--- a/src/Orc.Theming.Tests/PublicApiFacts.Orc_Theming_HasNoBreakingChanges_Async.verified.txt
+++ b/src/Orc.Theming.Tests/PublicApiFacts.Orc_Theming_HasNoBreakingChanges_Async.verified.txt
@@ -142,6 +142,19 @@ namespace Orc.Theming
         public double Width { get; set; }
         protected override object ProvideDynamicValue(System.IServiceProvider? serviceProvider) { }
     }
+    public class FontSize : Catel.Windows.Markup.UpdatableMarkupExtension
+    {
+        public FontSize() { }
+        [System.Windows.Markup.ConstructorArgument("delta")]
+        public double? Delta { get; set; }
+        [System.Windows.Markup.ConstructorArgument("scale")]
+        public double? Scale { get; set; }
+        [System.Windows.Markup.ConstructorArgument("subscribeToEvents")]
+        public bool SubscribeToEvents { get; set; }
+        protected override void OnTargetObjectLoaded() { }
+        protected override void OnTargetObjectUnloaded() { }
+        protected override object? ProvideDynamicValue(System.IServiceProvider? serviceProvider) { }
+    }
     public class FontSizeService : Orc.Theming.IFontSizeService
     {
         public FontSizeService() { }
diff --git a/src/Orc.Theming/Markup/FontSize.cs b/src/Orc.Theming/Markup/FontSize.cs
new file mode 100644
index 0000000..c19aa35
--- /dev/null
+++ b/src/Orc.Theming/Markup/FontSize.cs
@@ -0,0 +1,119 @@
+namespace Orc.Theming;
+
+using System;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Markup;
+using Catel.IoC;
+using Catel.Logging;
+using Catel.Windows;
+using Catel.Windows.Markup;
+
+/// <summary>
+/// Markup extension that can set a relative font size.
+/// </summary>
+public class FontSize : UpdatableMarkupExtension
+{
+    private static readonly ILog Log = LogManager.GetCurrentClassLogger();
+
+    private IFontSizeService? _fontSizeService;
+
+    static FontSize()
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="FontSize" /> class.
+    /// </summary>
+    public FontSize()
+    {
+        Scale = 1.0d;
+        SubscribeToEvents = false;
+    }
+
+    /// <summary>
+    /// Gets or sets the font size scaling.
+    /// </summary>
+    /// <value>The font size scaling.</value>
+    [ConstructorArgument("scale")]
+    public double? Scale { get; set; }
+
+    /// <summary>
+    /// Gets or sets the font size delta.
+    /// </summary>
+    /// <value>The font size delta.</value>
+    [ConstructorArgument("delta")]
+    public double? Delta { get; set; }
+
+    /// <summary>
+    /// Gets or sets whether this markup extension should subscribe to events to be responsive.
+    /// <para />
+    /// The default value is <c>false</c> for performance reasons.
+    /// </summary>
+    /// <value>The font size delta.</value>
+    [ConstructorArgument("subscribeToEvents")]
+    public bool SubscribeToEvents { get; set; }
+
+    protected override object? ProvideDynamicValue(IServiceProvider? serviceProvider)
+    {
+        var defaultFontSize = 12d;
+
+        if (TargetObject is DependencyObject dependencyObject)
+        {
+            var parentControl = dependencyObject.GetLogicalParent()?.FindLogicalAncestorByType<Control>();
+            if (parentControl is not null)
+            {
+                defaultFontSize = (double)parentControl.GetValue(Control.FontSizeProperty);
+            }
+        }
+
+        var finalFontSize = defaultFontSize;
+
+        if (Delta is not null)
+        {
+            finalFontSize += Delta.Value;
+        }
+
+        if (Scale is not null)
+        {
+            finalFontSize *= Scale.Value;
+        }
+
+        return finalFontSize;
+    }
+
+    protected override void OnTargetObjectLoaded()
+    {
+        base.OnTargetObjectLoaded();
+
+        if (SubscribeToEvents)
+        {
+            var fontSizeService = _fontSizeService;
+            if (fontSizeService is null)
+            {
+                _fontSizeService = fontSizeService = ServiceLocator.Default.ResolveType<IFontSizeService>();
+            }
+
+            if (fontSizeService is not null)
+            {
+                fontSizeService.FontSizeChanged += OnFontSizeServiceFontSizeChanged;
+            }
+        }
+    }
+
+    protected override void OnTargetObjectUnloaded()
+    {
+        var fontSizeService = _fontSizeService;
+        if (fontSizeService is not null)
+        {
+            fontSizeService.FontSizeChanged -= OnFontSizeServiceFontSizeChanged;
+        }
+
+        base.OnTargetObjectUnloaded();
+    }
+
+    private void OnFontSizeServiceFontSizeChanged(object? sender, EventArgs e)
+    {
+        UpdateValue();
+    }
+}
diff --git a/src/Orc.Theming/ViewModels/FontSizeSwitcherViewModel.cs b/src/Orc.Theming/ViewModels/FontSizeSwitcherViewModel.cs
index 11c01b8..c098bd9 100644
--- a/src/Orc.Theming/ViewModels/FontSizeSwitcherViewModel.cs
+++ b/src/Orc.Theming/ViewModels/FontSizeSwitcherViewModel.cs
@@ -65,4 +65,4 @@ private void OnSelectedFontSizeChanged()
     {
         _fontSizeService.SetFontSize(SelectedFontSize);
     }
-}
\ No newline at end of file
+}