diff --git a/python/core/auto_generated/symbology/qgsgeometrygeneratorsymbollayer.sip.in b/python/core/auto_generated/symbology/qgsgeometrygeneratorsymbollayer.sip.in
index 8fcbfa1efc78..9de6e8960e58 100644
--- a/python/core/auto_generated/symbology/qgsgeometrygeneratorsymbollayer.sip.in
+++ b/python/core/auto_generated/symbology/qgsgeometrygeneratorsymbollayer.sip.in
@@ -70,6 +70,30 @@ Set the expression to generate this geometry.
     QString geometryExpression() const;
 %Docstring
 Gets the expression to generate this geometry.
+%End
+
+    QgsUnitTypes::RenderUnit units() const;
+%Docstring
+Returns the unit for the geometry expression.
+
+By default this is :py:class:`QgsUnitTypes`.MapUnits, which means that the :py:func:`~QgsGeometryGeneratorSymbolLayer.geometryExpression`
+will return geometries in the associated layer's CRS.
+
+.. seealso:: :py:func:`setUnits`
+
+.. versionadded:: 3.22
+%End
+
+    void setUnits( QgsUnitTypes::RenderUnit units );
+%Docstring
+Sets the ``units`` for the geometry expression.
+
+By default this is :py:class:`QgsUnitTypes`.MapUnits, which means that the :py:func:`~QgsGeometryGeneratorSymbolLayer.geometryExpression`
+will return geometries in the associated layer's CRS.
+
+.. seealso:: :py:func:`units`
+
+.. versionadded:: 3.22
 %End
 
     virtual QgsSymbol *subSymbol();
@@ -105,6 +129,7 @@ context which is available to the evaluated expression.
     virtual void setColor( const QColor &color );
 
 
+
   private:
     QgsGeometryGeneratorSymbolLayer( const QgsGeometryGeneratorSymbolLayer &copy );
 };
diff --git a/python/gui/auto_generated/qgsunitselectionwidget.sip.in b/python/gui/auto_generated/qgsunitselectionwidget.sip.in
index 2ef85c3591c6..991b7beaa05f 100644
--- a/python/gui/auto_generated/qgsunitselectionwidget.sip.in
+++ b/python/gui/auto_generated/qgsunitselectionwidget.sip.in
@@ -222,6 +222,24 @@ map scale from the canvas.
 :param canvas: map canvas
 
 .. versionadded:: 2.12
+%End
+
+    bool showMapScaleButton() const;
+%Docstring
+Returns ``True`` if the widget can show the map scale button when the Map Units option is selected.
+
+.. seealso:: :py:func:`setShowMapScaleButton`
+
+.. versionadded:: 3.22
+%End
+
+    void setShowMapScaleButton( bool show );
+%Docstring
+Sets whether the widget can show the map scale button when the Map Units option is selected.
+
+.. seealso:: :py:func:`showMapScaleButton`
+
+.. versionadded:: 3.22
 %End
 
   signals:
diff --git a/src/core/symbology/qgsgeometrygeneratorsymbollayer.cpp b/src/core/symbology/qgsgeometrygeneratorsymbollayer.cpp
index bd42d7d62095..f2d6eefef066 100644
--- a/src/core/symbology/qgsgeometrygeneratorsymbollayer.cpp
+++ b/src/core/symbology/qgsgeometrygeneratorsymbollayer.cpp
@@ -42,6 +42,8 @@ QgsSymbolLayer *QgsGeometryGeneratorSymbolLayer::create( const QVariantMap &prop
   {
     symbolLayer->setSubSymbol( QgsFillSymbol::createSimple( properties ) );
   }
+  symbolLayer->setUnits( QgsUnitTypes::decodeRenderUnit( properties.value( QStringLiteral( "units" ), QStringLiteral( "mapunits" ) ).toString() ) );
+
   symbolLayer->restoreOldDataDefinedProperties( properties );
 
   return symbolLayer;
@@ -133,6 +135,7 @@ QgsSymbolLayer *QgsGeometryGeneratorSymbolLayer::clone() const
     clone->mMarkerSymbol.reset( mMarkerSymbol->clone() );
 
   clone->setSymbolType( mSymbolType );
+  clone->setUnits( mUnits );
 
   copyDataDefinedProperties( clone );
   copyPaintEffect( clone );
@@ -156,6 +159,8 @@ QVariantMap QgsGeometryGeneratorSymbolLayer::properties() const
       props.insert( QStringLiteral( "SymbolType" ), QStringLiteral( "Fill" ) );
       break;
   }
+  props.insert( QStringLiteral( "units" ), QgsUnitTypes::encodeUnit( mUnits ) );
+
   return props;
 }
 
@@ -222,11 +227,55 @@ void QgsGeometryGeneratorSymbolLayer::render( QgsSymbolRenderContext &context )
 
   if ( context.feature() )
   {
-    const QgsExpressionContext &expressionContext = context.renderContext().expressionContext();
+    QgsExpressionContext &expressionContext = context.renderContext().expressionContext();
 
     QgsFeature f = expressionContext.feature();
-    const QgsGeometry geom = mExpression->evaluate( &expressionContext ).value<QgsGeometry>();
-    f.setGeometry( geom );
+
+    switch ( mUnits )
+    {
+      case QgsUnitTypes::RenderMapUnits:
+      case QgsUnitTypes::RenderUnknownUnit: // unsupported, not exposed as an option
+      case QgsUnitTypes::RenderMetersInMapUnits: // unsupported, not exposed as an option
+      case QgsUnitTypes::RenderPercentage: // unsupported, not exposed as an option
+      {
+        QgsGeometry geom = mExpression->evaluate( &expressionContext ).value<QgsGeometry>();
+        f.setGeometry( geom );
+        break;
+      }
+
+      case QgsUnitTypes::RenderMillimeters:
+      case QgsUnitTypes::RenderPixels:
+      case QgsUnitTypes::RenderPoints:
+      case QgsUnitTypes::RenderInches:
+      {
+        QgsExpressionContextScope *generatorScope = new QgsExpressionContextScope();
+        expressionContext.appendScope( generatorScope );
+
+        QgsGeometry transformed = f.geometry();
+        transformed.transform( context.renderContext().coordinateTransform() );
+        QTransform mapToPixel = context.renderContext().mapToPixel().transform();
+
+        // scale transform to target units
+        const double scale = 1 / context.renderContext().convertToPainterUnits( 1, mUnits );
+        mapToPixel.scale( scale, scale );
+
+        if ( mExpression->referencedVariables().contains( QStringLiteral( "map_geometry" ) ) )
+        {
+          transformed.transform( mapToPixel );
+          generatorScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "map_geometry" ), transformed ) );
+        }
+
+        QgsGeometry geom = mExpression->evaluate( &expressionContext ).value<QgsGeometry>();
+
+        geom.transform( mapToPixel.inverted() );
+        geom.transform( context.renderContext().coordinateTransform(), QgsCoordinateTransform::ReverseTransform );
+
+        f.setGeometry( geom );
+
+        delete expressionContext.popScope();
+        break;
+      }
+    }
 
     QgsExpressionContextScope *subSymbolExpressionContextScope = mSymbol->symbolRenderContext()->expressionContextScope();
 
diff --git a/src/core/symbology/qgsgeometrygeneratorsymbollayer.h b/src/core/symbology/qgsgeometrygeneratorsymbollayer.h
index 80f4e67932a4..5cc3174999ac 100644
--- a/src/core/symbology/qgsgeometrygeneratorsymbollayer.h
+++ b/src/core/symbology/qgsgeometrygeneratorsymbollayer.h
@@ -76,6 +76,28 @@ class CORE_EXPORT QgsGeometryGeneratorSymbolLayer : public QgsSymbolLayer
      */
     QString geometryExpression() const { return mExpression->expression(); }
 
+    /**
+     * Returns the unit for the geometry expression.
+     *
+     * By default this is QgsUnitTypes::MapUnits, which means that the geometryExpression()
+     * will return geometries in the associated layer's CRS.
+     *
+     * \see setUnits()
+     * \since QGIS 3.22
+     */
+    QgsUnitTypes::RenderUnit units() const { return mUnits; }
+
+    /**
+     * Sets the \a units for the geometry expression.
+     *
+     * By default this is QgsUnitTypes::MapUnits, which means that the geometryExpression()
+     * will return geometries in the associated layer's CRS.
+     *
+     * \see units()
+     * \since QGIS 3.22
+     */
+    void setUnits( QgsUnitTypes::RenderUnit units ) { mUnits = units;}
+
     QgsSymbol *subSymbol() override { return mSymbol; }
 
     bool setSubSymbol( QgsSymbol *symbol SIP_TRANSFER ) override;
@@ -104,6 +126,7 @@ class CORE_EXPORT QgsGeometryGeneratorSymbolLayer : public QgsSymbolLayer
 
     void setColor( const QColor &color ) override;
 
+
   private:
     QgsGeometryGeneratorSymbolLayer( const QString &expression );
 
@@ -122,6 +145,8 @@ class CORE_EXPORT QgsGeometryGeneratorSymbolLayer : public QgsSymbolLayer
      */
     Qgis::SymbolType mSymbolType;
 
+    QgsUnitTypes::RenderUnit mUnits = QgsUnitTypes::RenderMapUnits;
+
     bool mRenderingFeature = false;
     bool mHasRenderedFeature = false;
 };
diff --git a/src/gui/qgsunitselectionwidget.cpp b/src/gui/qgsunitselectionwidget.cpp
index f439d46b8ce1..4c077dafb72a 100644
--- a/src/gui/qgsunitselectionwidget.cpp
+++ b/src/gui/qgsunitselectionwidget.cpp
@@ -252,11 +252,11 @@ void QgsUnitSelectionWidget::toggleUnitRangeButton()
 {
   if ( unit() != QgsUnitTypes::RenderUnknownUnit )
   {
-    mMapScaleButton->setVisible( unit() == QgsUnitTypes::RenderMapUnits );
+    mMapScaleButton->setVisible( mShowMapScaleButton && unit() == QgsUnitTypes::RenderMapUnits );
   }
   else
   {
-    mMapScaleButton->setVisible( mMapUnitIdx != -1 && mUnitCombo->currentIndex() == mMapUnitIdx );
+    mMapScaleButton->setVisible( mShowMapScaleButton && mMapUnitIdx != -1 && mUnitCombo->currentIndex() == mMapUnitIdx );
   }
 }
 
@@ -266,6 +266,18 @@ void QgsUnitSelectionWidget::widgetChanged( const QgsMapUnitScale &scale )
   emit changed();
 }
 
+bool QgsUnitSelectionWidget::showMapScaleButton() const
+{
+  return mShowMapScaleButton;
+}
+
+void QgsUnitSelectionWidget::setShowMapScaleButton( bool show )
+{
+  mShowMapScaleButton = show;
+  if ( !show )
+    mMapScaleButton->hide();
+}
+
 
 QgsMapUnitScaleDialog::QgsMapUnitScaleDialog( QWidget *parent )
   : QDialog( parent )
diff --git a/src/gui/qgsunitselectionwidget.h b/src/gui/qgsunitselectionwidget.h
index a00f1f92960c..1d8dfabe9402 100644
--- a/src/gui/qgsunitselectionwidget.h
+++ b/src/gui/qgsunitselectionwidget.h
@@ -225,6 +225,22 @@ class GUI_EXPORT QgsUnitSelectionWidget : public QWidget, private Ui::QgsUnitSel
      */
     void setMapCanvas( QgsMapCanvas *canvas );
 
+    /**
+     * Returns TRUE if the widget can show the map scale button when the Map Units option is selected.
+     *
+     * \see setShowMapScaleButton()
+     * \since QGIS 3.22
+     */
+    bool showMapScaleButton() const;
+
+    /**
+     * Sets whether the widget can show the map scale button when the Map Units option is selected.
+     *
+     * \see showMapScaleButton()
+     * \since QGIS 3.22
+     */
+    void setShowMapScaleButton( bool show );
+
   signals:
     void changed();
 
@@ -237,6 +253,7 @@ class GUI_EXPORT QgsUnitSelectionWidget : public QWidget, private Ui::QgsUnitSel
     QgsMapUnitScale mMapUnitScale;
     int mMapUnitIdx;
     QgsMapCanvas *mCanvas = nullptr;
+    bool mShowMapScaleButton = true;
 
 };
 
diff --git a/src/gui/symbology/qgssymbollayerwidget.cpp b/src/gui/symbology/qgssymbollayerwidget.cpp
index bbe4a5d7b115..e36798016ead 100644
--- a/src/gui/symbology/qgssymbollayerwidget.cpp
+++ b/src/gui/symbology/qgssymbollayerwidget.cpp
@@ -4288,15 +4288,35 @@ QgsGeometryGeneratorSymbolLayerWidget::QgsGeometryGeneratorSymbolLayerWidget( Qg
   cbxGeometryType->addItem( QgsIconUtils::iconPolygon(), tr( "Polygon / MultiPolygon" ), static_cast< int >( Qgis::SymbolType::Fill ) );
   cbxGeometryType->addItem( QgsIconUtils::iconLine(), tr( "LineString / MultiLineString" ), static_cast< int >( Qgis::SymbolType::Line ) );
   cbxGeometryType->addItem( QgsIconUtils::iconPoint(), tr( "Point / MultiPoint" ), static_cast< int >( Qgis::SymbolType::Marker ) );
+
+  mUnitWidget->setUnits( {QgsUnitTypes::RenderMillimeters,
+                          QgsUnitTypes::RenderPoints,
+                          QgsUnitTypes::RenderPixels,
+                          QgsUnitTypes::RenderInches,
+                          QgsUnitTypes::RenderMapUnits
+                         } );
+  mUnitWidget->setShowMapScaleButton( false );
+
   connect( modificationExpressionSelector, &QgsExpressionLineEdit::expressionChanged, this, &QgsGeometryGeneratorSymbolLayerWidget::updateExpression );
   connect( cbxGeometryType, static_cast<void ( QComboBox::* )( int )>( &QComboBox::currentIndexChanged ), this, &QgsGeometryGeneratorSymbolLayerWidget::updateSymbolType );
+  connect( mUnitWidget, &QgsUnitSelectionWidget::changed, this, [ = ]
+  {
+    if ( !mBlockSignals )
+    {
+      mLayer->setUnits( mUnitWidget->unit() );
+      emit symbolChanged();
+    }
+  } );
 }
 
 void QgsGeometryGeneratorSymbolLayerWidget::setSymbolLayer( QgsSymbolLayer *l )
 {
+  mBlockSignals++;
   mLayer = static_cast<QgsGeometryGeneratorSymbolLayer *>( l );
   modificationExpressionSelector->setExpression( mLayer->geometryExpression() );
   cbxGeometryType->setCurrentIndex( cbxGeometryType->findData( static_cast< int >( mLayer->symbolType() ) ) );
+  mUnitWidget->setUnit( mLayer->units() );
+  mBlockSignals--;
 }
 
 QgsSymbolLayer *QgsGeometryGeneratorSymbolLayerWidget::symbolLayer()
diff --git a/src/gui/symbology/qgssymbollayerwidget.h b/src/gui/symbology/qgssymbollayerwidget.h
index 270d046f9d61..cfb97d70a909 100644
--- a/src/gui/symbology/qgssymbollayerwidget.h
+++ b/src/gui/symbology/qgssymbollayerwidget.h
@@ -1138,6 +1138,7 @@ class GUI_EXPORT QgsGeometryGeneratorSymbolLayerWidget : public QgsSymbolLayerWi
 
   private:
     QgsGeometryGeneratorSymbolLayer *mLayer = nullptr;
+    int mBlockSignals = 0;
 
   private slots:
     void updateExpression( const QString &string );
diff --git a/src/ui/symbollayer/qgsgeometrygeneratorwidgetbase.ui b/src/ui/symbollayer/qgsgeometrygeneratorwidgetbase.ui
index c64b81dc8054..ef82faae108d 100644
--- a/src/ui/symbollayer/qgsgeometrygeneratorwidgetbase.ui
+++ b/src/ui/symbollayer/qgsgeometrygeneratorwidgetbase.ui
@@ -13,12 +13,16 @@
   <property name="windowTitle">
    <string notr="true">Form</string>
   </property>
-  <layout class="QGridLayout" name="gridLayout">
-   <item row="1" column="0" colspan="2">
+  <layout class="QGridLayout" name="gridLayout" rowstretch="0,0,1">
+   <item row="2" column="0" colspan="2">
     <widget class="QgsExpressionLineEdit" name="modificationExpressionSelector" native="true"/>
    </item>
-   <item row="0" column="1">
-    <widget class="QComboBox" name="cbxGeometryType"/>
+   <item row="1" column="0">
+    <widget class="QLabel" name="label_2">
+     <property name="text">
+      <string>Units</string>
+     </property>
+    </widget>
    </item>
    <item row="0" column="0">
     <widget class="QLabel" name="label">
@@ -33,6 +37,22 @@
      </property>
     </widget>
    </item>
+   <item row="1" column="1">
+    <widget class="QgsUnitSelectionWidget" name="mUnitWidget" native="true">
+     <property name="minimumSize">
+      <size>
+       <width>0</width>
+       <height>0</height>
+      </size>
+     </property>
+     <property name="focusPolicy">
+      <enum>Qt::StrongFocus</enum>
+     </property>
+    </widget>
+   </item>
+   <item row="0" column="1">
+    <widget class="QComboBox" name="cbxGeometryType"/>
+   </item>
   </layout>
  </widget>
  <customwidgets>
@@ -42,6 +62,12 @@
    <header>qgsexpressionlineedit.h</header>
    <container>1</container>
   </customwidget>
+  <customwidget>
+   <class>QgsUnitSelectionWidget</class>
+   <extends>QWidget</extends>
+   <header>qgsunitselectionwidget.h</header>
+   <container>1</container>
+  </customwidget>
  </customwidgets>
  <resources/>
  <connections/>