diff --git a/packages/react-native-fantom/src/__tests__/Fantom-itest.js b/packages/react-native-fantom/src/__tests__/Fantom-itest.js
index f16d30bd10fbee..97c65c8eaa6616 100644
--- a/packages/react-native-fantom/src/__tests__/Fantom-itest.js
+++ b/packages/react-native-fantom/src/__tests__/Fantom-itest.js
@@ -7,13 +7,47 @@
  * @flow strict-local
  * @format
  * @oncall react_native
+ * @fantom_flags enableAccessToHostTreeInFabric:true
  */
 
 import 'react-native/Libraries/Core/InitializeCore';
 
+import type {Root} from '..';
+
 import {createRoot, runTask} from '..';
 import * as React from 'react';
 import {Text, View} from 'react-native';
+import ReactNativeElement from 'react-native/src/private/webapis/dom/nodes/ReactNativeElement';
+
+function getActualViewportDimensions(root: Root): {
+  viewportWidth: number,
+  viewportHeight: number,
+} {
+  let maybeNode;
+
+  runTask(() => {
+    root.render(
+      <View
+        style={{width: '100%', height: '100%'}}
+        ref={node => {
+          maybeNode = node;
+        }}
+      />,
+    );
+  });
+
+  if (!(maybeNode instanceof ReactNativeElement)) {
+    throw new Error(
+      `Expected instance of ReactNativeElement but got ${String(maybeNode)}`,
+    );
+  }
+
+  const rect = maybeNode.getBoundingClientRect();
+  return {
+    viewportWidth: rect.width,
+    viewportHeight: rect.height,
+  };
+}
 
 describe('Fantom', () => {
   describe('runTask', () => {
@@ -101,6 +135,29 @@ describe('Fantom', () => {
     });
   });
 
+  describe('createRoot', () => {
+    it('allows creating a root with specific dimensions', () => {
+      const rootWithDefaults = createRoot();
+
+      expect(getActualViewportDimensions(rootWithDefaults)).toEqual({
+        viewportWidth: 1000,
+        viewportHeight: 1000,
+      });
+
+      const rootWithCustomWidthAndHeight = createRoot({
+        viewportWidth: 200,
+        viewportHeight: 600,
+      });
+
+      expect(getActualViewportDimensions(rootWithCustomWidthAndHeight)).toEqual(
+        {
+          viewportWidth: 200,
+          viewportHeight: 600,
+        },
+      );
+    });
+  });
+
   describe('getRenderedOutput', () => {
     describe('toJSX', () => {
       it('default config', () => {
diff --git a/packages/react-native-fantom/src/index.js b/packages/react-native-fantom/src/index.js
index 67795cc5c67f79..92e0bf0558ffdc 100644
--- a/packages/react-native-fantom/src/index.js
+++ b/packages/react-native-fantom/src/index.js
@@ -24,18 +24,41 @@ const nativeRuntimeScheduler = global.nativeRuntimeScheduler;
 const schedulerPriorityImmediate =
   nativeRuntimeScheduler.unstable_ImmediatePriority;
 
+export type RootConfig = {
+  viewportWidth?: number,
+  viewportHeight?: number,
+  devicePixelRatio?: number,
+};
+
+const DEFAULT_VIEWPORT_WIDTH = 1000;
+const DEFAULT_VIEWPORT_HEIGHT = 1000;
+const DEFAULT_DEVICE_PIXEL_RATIO = 1;
+
 class Root {
   #surfaceId: number;
+  #viewportWidth: number;
+  #viewportHeight: number;
+  #devicePixelRatio: number;
+
   #hasRendered: boolean = false;
 
-  constructor() {
+  constructor(config?: RootConfig) {
     this.#surfaceId = globalSurfaceIdCounter;
+    this.#viewportWidth = config?.viewportWidth ?? DEFAULT_VIEWPORT_WIDTH;
+    this.#viewportHeight = config?.viewportHeight ?? DEFAULT_VIEWPORT_HEIGHT;
+    this.#devicePixelRatio =
+      config?.devicePixelRatio ?? DEFAULT_DEVICE_PIXEL_RATIO;
     globalSurfaceIdCounter += 10;
   }
 
   render(element: MixedElement) {
     if (!this.#hasRendered) {
-      NativeFantom.startSurface(this.#surfaceId);
+      NativeFantom.startSurface(
+        this.#surfaceId,
+        this.#viewportWidth,
+        this.#viewportHeight,
+        this.#devicePixelRatio,
+      );
       this.#hasRendered = true;
     }
 
@@ -59,6 +82,8 @@ class Root {
   // TODO: add an API to check if all surfaces were deallocated when tests are finished.
 }
 
+export type {Root};
+
 const DEFAULT_TASK_PRIORITY = schedulerPriorityImmediate;
 
 /**
@@ -108,6 +133,6 @@ export function runWorkLoop(): void {
 
 // TODO: Add option to define surface props and pass it to startSurface
 // Surfacep rops: concurrentRoot, surfaceWidth, surfaceHeight, layoutDirection, pointScaleFactor.
-export function createRoot(): Root {
-  return new Root();
+export function createRoot(rootConfig?: RootConfig): Root {
+  return new Root(rootConfig);
 }
diff --git a/packages/react-native/src/private/specs/modules/NativeFantom.js b/packages/react-native/src/private/specs/modules/NativeFantom.js
index 34c04f2eaebf61..f4b5ce24d49b3a 100644
--- a/packages/react-native/src/private/specs/modules/NativeFantom.js
+++ b/packages/react-native/src/private/specs/modules/NativeFantom.js
@@ -19,7 +19,12 @@ export type RenderFormatOptions = {
 };
 
 interface Spec extends TurboModule {
-  startSurface: (surfaceId: number) => void;
+  startSurface: (
+    surfaceId: number,
+    viewportWidth: number,
+    viewportHeight: number,
+    devicePixelRatio: number,
+  ) => void;
   stopSurface: (surfaceId: number) => void;
   getMountingManagerLogs: (surfaceId: number) => Array<string>;
   flushMessageQueue: () => void;