diff --git a/main_wayland.cpp b/main_wayland.cpp
--- a/main_wayland.cpp
+++ b/main_wayland.cpp
@@ -527,6 +527,12 @@
                                     i18n("The height for windowed mode. Default height is 768."),
                                     QStringLiteral("height"));
     heightOption.setDefaultValue(QString::number(768));
+
+    QCommandLineOption scaleOption(QStringLiteral("scale"),
+                                    i18n("The scale for windowed mode. Default value is 1."),
+                                    QStringLiteral("scale"));
+    scaleOption.setDefaultValue(QString::number(1));
+
     QCommandLineOption outputCountOption(QStringLiteral("output-count"),
                                     i18n("The number of windows to open as outputs in windowed mode. Default value is 1"),
                                     QStringLiteral("height"));
@@ -555,6 +561,7 @@
     if (hasSizeOption) {
         parser.addOption(widthOption);
         parser.addOption(heightOption);
+        parser.addOption(scaleOption);
     }
     if (hasOutputCountOption) {
         parser.addOption(outputCountOption);
@@ -633,6 +640,7 @@
     QSize initialWindowSize;
     QByteArray deviceIdentifier;
     int outputCount = 1;
+    qreal outputScale = 1;
 
 #if HAVE_DRM
     if (hasDrmOption && parser.isSet(drmOption)) {
@@ -652,6 +660,13 @@
             std::cerr << "FATAL ERROR incorrect value for height" << std::endl;
             return 1;
         }
+        const qreal scale = parser.value(scaleOption).toDouble(&ok);
+        if (!ok || scale < 1) {
+            std::cerr << "FATAL ERROR incorrect value for scale" << std::endl;
+            return 1;
+        }
+
+        outputScale = scale;
         initialWindowSize = QSize(width, height);
     }
 
@@ -733,6 +748,7 @@
     if (initialWindowSize.isValid()) {
         a.platform()->setInitialWindowSize(initialWindowSize);
     }
+    a.platform()->setInitialOutputScale(outputScale);
     a.platform()->setInitialOutputCount(outputCount);
 
     QObject::connect(&a, &KWin::Application::workspaceCreated, server, &KWin::WaylandServer::initWorkspace);
diff --git a/platform.h b/platform.h
--- a/platform.h
+++ b/platform.h
@@ -104,6 +104,14 @@
      * Base implementation returns one QRect positioned at 0/0 with screenSize() as size.
      **/
     virtual QVector<QRect> screenGeometries() const;
+
+    /**
+     * Implementing subclasses should provide all geometries in case the backend represents
+     * a basic screen and uses the BasicScreens.
+     *
+     * Base implementation returns a screen with a scale of 1.
+     **/
+    virtual QVector<qreal> screenScales() const;
     /**
      * Implement this method to receive configuration change requests through KWayland's
      * OutputManagement interface.
@@ -268,6 +276,12 @@
     void setInitialOutputCount(int count) {
         m_initialOutputCount = count;
     }
+    qreal initialOutputScale() const {
+        return m_initialOutputScale;
+    }
+    void setInitialOutputScale(qreal scale) {
+        m_initialOutputScale = scale;
+    }
 
 public Q_SLOTS:
     void pointerMotion(const QPointF &position, quint32 time);
@@ -350,6 +364,7 @@
     bool m_pointerWarping = false;
     bool m_outputsEnabled = true;
     int m_initialOutputCount = 1;
+    qreal m_initialOutputScale = 1;
     EGLDisplay m_eglDisplay;
     int m_hideCursorCounter = 0;
 };
diff --git a/platform.cpp b/platform.cpp
--- a/platform.cpp
+++ b/platform.cpp
@@ -343,6 +343,11 @@
     return QVector<QRect>({QRect(QPoint(0, 0), screenSize())});
 }
 
+QVector<qreal> Platform::screenScales() const
+{
+    return QVector<qreal>({1});
+}
+
 bool Platform::requiresCompositing() const
 {
     return true;
diff --git a/plugins/platforms/x11/windowed/x11windowed_backend.h b/plugins/platforms/x11/windowed/x11windowed_backend.h
--- a/plugins/platforms/x11/windowed/x11windowed_backend.h
+++ b/plugins/platforms/x11/windowed/x11windowed_backend.h
@@ -47,6 +47,7 @@
     virtual ~X11WindowedBackend();
     void init() override;
     QVector<QRect> screenGeometries() const override;
+    QVector<qreal> screenScales() const override;
 
     xcb_connection_t *connection() const {
         return m_connection;
diff --git a/plugins/platforms/x11/windowed/x11windowed_backend.cpp b/plugins/platforms/x11/windowed/x11windowed_backend.cpp
--- a/plugins/platforms/x11/windowed/x11windowed_backend.cpp
+++ b/plugins/platforms/x11/windowed/x11windowed_backend.cpp
@@ -472,4 +472,11 @@
     return ret;
 }
 
+QVector<qreal> X11WindowedBackend::screenScales() const
+{
+    QVector<qreal> ret;
+    ret.fill(initialOutputScale(), m_windows.count());
+    return ret;
+}
+
 }
diff --git a/screens.h b/screens.h
--- a/screens.h
+++ b/screens.h
@@ -86,6 +86,11 @@
      * @see size()
      **/
     virtual QSize size(int screen) const = 0;
+
+    /*
+     * The output scale for this display, for use by high DPI displays
+     */
+    virtual qreal scale(int screen) const;
     /**
      * The bounding size of all screens combined. Overlapping areas
      * are not counted multiple times.
@@ -164,11 +169,13 @@
     QRect geometry(int screen) const override;
     int number(const QPoint &pos) const override;
     QSize size(int screen) const override;
+    qreal scale(int screen) const override;
     void updateCount() override;
 
 private:
     Platform *m_backend;
     QVector<QRect> m_geometries;
+    QVector<qreal> m_scales;
 };
 
 inline
diff --git a/screens.cpp b/screens.cpp
--- a/screens.cpp
+++ b/screens.cpp
@@ -91,6 +91,13 @@
     return 60.0f;
 }
 
+qreal Screens::scale(int screen) const
+{
+    Q_UNUSED(screen)
+    qCWarning(KWIN_CORE, "%s::scale(qreal screen) is a stub, please reimplement it!", metaObject()->className());
+    return 1;
+}
+
 void Screens::reconfigure()
 {
     if (!m_config) {
@@ -213,9 +220,18 @@
     return QSize();
 }
 
+qreal BasicScreens::scale(int screen) const
+{
+    if (screen < m_scales.count()) {
+        return m_scales.at(screen);
+    }
+    return 1;
+}
+
 void BasicScreens::updateCount()
 {
     m_geometries = m_backend->screenGeometries();
+    m_scales = m_backend->screenScales();
     setCount(m_geometries.count());
 }
 
diff --git a/wayland_server.cpp b/wayland_server.cpp
--- a/wayland_server.cpp
+++ b/wayland_server.cpp
@@ -352,6 +352,7 @@
     Q_ASSERT(s);
     for (int i = 0; i < s->count(); ++i) {
         OutputInterface *output = m_display->createOutput(m_display);
+        output->setScale(s->scale(i));
         const QRect &geo = s->geometry(i);
         output->setGlobalPosition(geo.topLeft());
         output->setPhysicalSize(geo.size() / 3.8);