diff --git a/autotests/mockclient.h b/autotests/mockclient.h
--- a/autotests/mockclient.h
+++ b/autotests/mockclient.h
@@ -67,6 +67,7 @@
     void requestToggleShade() override;
     void requestShowToolTip(const QString &text) override;
     void requestHideToolTip() override;
+    QSize size() const override;
     int width() const override;
     WId windowId() const override;
 
diff --git a/autotests/mockclient.cpp b/autotests/mockclient.cpp
--- a/autotests/mockclient.cpp
+++ b/autotests/mockclient.cpp
@@ -242,6 +242,11 @@
 
 }
 
+QSize MockClient::size() const
+{
+    return QSize(m_width, m_height);
+}
+
 int MockClient::width() const
 {
     return m_width;
diff --git a/src/decoratedclient.h b/src/decoratedclient.h
--- a/src/decoratedclient.h
+++ b/src/decoratedclient.h
@@ -157,6 +157,10 @@
      * The height of the DecoratedClient.
      **/
     Q_PROPERTY(int height READ height NOTIFY heightChanged)
+    /**
+     * The size of the DecoratedClient.
+     **/
+    Q_PROPERTY(QSize size READ size NOTIFY sizeChanged)
     /**
      * The palette this DecoratedClient uses. The palette might be different for each
      * DecoratedClient and the Decoration should honor the palette.
@@ -212,6 +216,7 @@
 
     int width() const;
     int height() const;
+    QSize size() const;
 
     QPointer<Decoration> decoration() const;
     QPalette palette() const;
@@ -273,6 +278,7 @@
 
     void widthChanged(int);
     void heightChanged(int);
+    void sizeChanged(const QSize &size);
     void paletteChanged(const QPalette &palette);
     void adjacentScreenEdgesChanged(Qt::Edges edges);
 
diff --git a/src/decoratedclient.cpp b/src/decoratedclient.cpp
--- a/src/decoratedclient.cpp
+++ b/src/decoratedclient.cpp
@@ -64,6 +64,7 @@
 DELEGATE(WId, decorationId)
 DELEGATE(int, width)
 DELEGATE(int, height)
+DELEGATE(QSize, size)
 DELEGATE(QPalette, palette)
 DELEGATE(Qt::Edges, adjacentScreenEdges)
 
diff --git a/src/private/CMakeLists.txt b/src/private/CMakeLists.txt
--- a/src/private/CMakeLists.txt
+++ b/src/private/CMakeLists.txt
@@ -25,7 +25,7 @@
 target_include_directories(kdecorations2private INTERFACE "$<INSTALL_INTERFACE:${KDECORATION2_INCLUDEDIR}>" )
 
 set_target_properties(kdecorations2private PROPERTIES VERSION   ${KDECORATION2_VERSION_STRING}
-                                                      SOVERSION 6
+                                                      SOVERSION 7
                                                       EXPORT_NAME KDecoration2Private
 )
 
diff --git a/src/private/decoratedclientprivate.h b/src/private/decoratedclientprivate.h
--- a/src/private/decoratedclientprivate.h
+++ b/src/private/decoratedclientprivate.h
@@ -73,6 +73,7 @@
 
     virtual int width() const = 0;
     virtual int height() const = 0;
+    virtual QSize size() const = 0;
     virtual QPalette palette() const = 0;
     virtual Qt::Edges adjacentScreenEdges() const = 0;