diff --git a/packages/virtualized-lists/Lists/__tests__/ListMetricsAggregator-test.js b/packages/virtualized-lists/Lists/__tests__/ListMetricsAggregator-test.js
index 6bbf4c3b99c..d36930d9b01 100644
--- a/packages/virtualized-lists/Lists/__tests__/ListMetricsAggregator-test.js
+++ b/packages/virtualized-lists/Lists/__tests__/ListMetricsAggregator-test.js
@@ -126,4 +126,590 @@ describe('ListMetricsAggregator', () => {
     });
     expect(listMetrics.getHighestMeasuredCellIndex()).toEqual(1);
   });
+
+  it('resets measurements if list orientation changes', () => {
+    const listMetrics = new ListMetricsAggregator();
+    expect(listMetrics.getAverageCellLength()).toEqual(0);
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 0,
+      cellKey: '0',
+      orientation: {horizontal: false, rtl: false},
+      layout: {
+        height: 10,
+        width: 5,
+        x: 0,
+        y: 0,
+      },
+    });
+    expect(listMetrics.getAverageCellLength()).toEqual(10);
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 1,
+      cellKey: '1',
+      orientation: {horizontal: true, rtl: false},
+      layout: {
+        height: 20,
+        width: 5,
+        x: 0,
+        y: 10,
+      },
+    });
+    expect(listMetrics.getAverageCellLength()).toEqual(5);
+  });
+
+  it('resolves metrics of already measured cell', () => {
+    const listMetrics = new ListMetricsAggregator();
+    const orientation = {horizontal: false, rtl: false};
+    const props: CellMetricProps = {
+      data: [1, 2, 3, 4, 5],
+      getItemCount: () => nullthrows(props.data).length,
+      getItem: (i: number) => nullthrows(props.data)[i],
+    };
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 0,
+      cellKey: '0',
+      orientation,
+      layout: {
+        height: 10,
+        width: 5,
+        x: 0,
+        y: 0,
+      },
+    });
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 1,
+      cellKey: '1',
+      orientation,
+      layout: {
+        height: 20,
+        width: 5,
+        x: 0,
+        y: 10,
+      },
+    });
+
+    expect(listMetrics.getCellMetrics(1, props)).toEqual({
+      index: 1,
+      length: 20,
+      offset: 10,
+      isMounted: true,
+    });
+    expect(listMetrics.getCellMetricsApprox(1, props)).toEqual({
+      index: 1,
+      length: 20,
+      offset: 10,
+      isMounted: true,
+    });
+  });
+
+  it('estimates metrics of unmeasured cell', () => {
+    const listMetrics = new ListMetricsAggregator();
+    const orientation = {horizontal: false, rtl: false};
+    const props: CellMetricProps = {
+      data: [1, 2, 3, 4, 5],
+      getItemCount: () => nullthrows(props.data).length,
+      getItem: (i: number) => nullthrows(props.data)[i],
+    };
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 0,
+      cellKey: '0',
+      orientation,
+      layout: {
+        height: 10,
+        width: 5,
+        x: 0,
+        y: 0,
+      },
+    });
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 1,
+      cellKey: '1',
+      orientation,
+      layout: {
+        height: 20,
+        width: 5,
+        x: 0,
+        y: 10,
+      },
+    });
+
+    expect(listMetrics.getCellMetrics(2, props)).toBeNull();
+    expect(listMetrics.getCellMetricsApprox(2, props)).toEqual({
+      index: 2,
+      length: 15,
+      offset: 30,
+      isMounted: false,
+    });
+  });
+
+  it('uses getItemLayout for metrics of unmeasured cell', () => {
+    const listMetrics = new ListMetricsAggregator();
+    const orientation = {horizontal: false, rtl: false};
+    const props: CellMetricProps = {
+      data: [1, 2, 3, 4, 5],
+      getItemCount: () => nullthrows(props.data).length,
+      getItem: (i: number) => nullthrows(props.data)[i],
+      getItemLayout: () => ({index: 2, length: 40, offset: 30}),
+    };
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 0,
+      cellKey: '0',
+      orientation,
+      layout: {
+        height: 10,
+        width: 5,
+        x: 0,
+        y: 0,
+      },
+    });
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 1,
+      cellKey: '1',
+      orientation,
+      layout: {
+        height: 20,
+        width: 5,
+        x: 0,
+        y: 10,
+      },
+    });
+
+    expect(listMetrics.getCellMetrics(2, props)).toMatchObject({
+      index: 2,
+      length: 40,
+      offset: 30,
+    });
+    expect(listMetrics.getCellMetricsApprox(2, props)).toMatchObject({
+      index: 2,
+      length: 40,
+      offset: 30,
+    });
+  });
+
+  it('resolves horizontal metrics of already measured cell', () => {
+    const listMetrics = new ListMetricsAggregator();
+    const orientation = {horizontal: true, rtl: false};
+    const props: CellMetricProps = {
+      data: [1, 2, 3, 4, 5],
+      getItemCount: () => nullthrows(props.data).length,
+      getItem: (i: number) => nullthrows(props.data)[i],
+    };
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 0,
+      cellKey: '0',
+      orientation,
+      layout: {
+        height: 5,
+        width: 10,
+        x: 0,
+        y: 0,
+      },
+    });
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 1,
+      cellKey: '1',
+      orientation,
+      layout: {
+        height: 5,
+        width: 20,
+        x: 10,
+        y: 0,
+      },
+    });
+
+    expect(listMetrics.getCellMetrics(1, props)).toEqual({
+      index: 1,
+      length: 20,
+      offset: 10,
+      isMounted: true,
+    });
+    expect(listMetrics.getCellMetricsApprox(1, props)).toEqual({
+      index: 1,
+      length: 20,
+      offset: 10,
+      isMounted: true,
+    });
+  });
+
+  it('estimates horizontal metrics of unmeasured cell', () => {
+    const listMetrics = new ListMetricsAggregator();
+    const orientation = {horizontal: true, rtl: false};
+    const props: CellMetricProps = {
+      data: [1, 2, 3, 4, 5],
+      getItemCount: () => nullthrows(props.data).length,
+      getItem: (i: number) => nullthrows(props.data)[i],
+    };
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 0,
+      cellKey: '0',
+      orientation,
+      layout: {
+        height: 5,
+        width: 10,
+        x: 0,
+        y: 0,
+      },
+    });
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 1,
+      cellKey: '1',
+      orientation,
+      layout: {
+        height: 5,
+        width: 20,
+        x: 10,
+        y: 0,
+      },
+    });
+
+    expect(listMetrics.getCellMetrics(2, props)).toBeNull();
+    expect(listMetrics.getCellMetricsApprox(2, props)).toEqual({
+      index: 2,
+      length: 15,
+      offset: 30,
+      isMounted: false,
+    });
+  });
+
+  it('uses getItemLayout for horizontal metrics of unmeasured cell', () => {
+    const listMetrics = new ListMetricsAggregator();
+    const orientation = {horizontal: true, rtl: false};
+    const props: CellMetricProps = {
+      data: [1, 2, 3, 4, 5],
+      getItemCount: () => nullthrows(props.data).length,
+      getItem: (i: number) => nullthrows(props.data)[i],
+      getItemLayout: () => ({index: 2, length: 40, offset: 30}),
+    };
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 0,
+      cellKey: '0',
+      orientation,
+      layout: {
+        height: 5,
+        width: 10,
+        x: 0,
+        y: 0,
+      },
+    });
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 1,
+      cellKey: '1',
+      orientation,
+      layout: {
+        height: 5,
+        width: 20,
+        x: 10,
+        y: 0,
+      },
+    });
+
+    expect(listMetrics.getCellMetrics(2, props)).toMatchObject({
+      index: 2,
+      length: 40,
+      offset: 30,
+    });
+    expect(listMetrics.getCellMetricsApprox(2, props)).toMatchObject({
+      index: 2,
+      length: 40,
+      offset: 30,
+    });
+  });
+
+  it('resolves RTL metrics of already measured cell', () => {
+    const listMetrics = new ListMetricsAggregator();
+    const orientation = {horizontal: true, rtl: true};
+    const props: CellMetricProps = {
+      data: [1, 2, 3, 4, 5],
+      getItemCount: () => nullthrows(props.data).length,
+      getItem: (i: number) => nullthrows(props.data)[i],
+    };
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 0,
+      cellKey: '0',
+      orientation,
+      layout: {
+        height: 5,
+        width: 10,
+        x: 90,
+        y: 0,
+      },
+    });
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 1,
+      cellKey: '1',
+      orientation,
+      layout: {
+        height: 5,
+        width: 20,
+        x: 70,
+        y: 0,
+      },
+    });
+
+    listMetrics.notifyListContentLayout({
+      layout: {width: 100, height: 5},
+      orientation,
+    });
+
+    expect(listMetrics.getCellMetrics(1, props)).toEqual({
+      index: 1,
+      length: 20,
+      offset: 10,
+      isMounted: true,
+    });
+    expect(listMetrics.getCellMetricsApprox(1, props)).toEqual({
+      index: 1,
+      length: 20,
+      offset: 10,
+      isMounted: true,
+    });
+  });
+
+  it('estimates RTL metrics of unmeasured cell', () => {
+    const listMetrics = new ListMetricsAggregator();
+    const orientation = {horizontal: true, rtl: false};
+    const props: CellMetricProps = {
+      data: [1, 2, 3, 4, 5],
+      getItemCount: () => nullthrows(props.data).length,
+      getItem: (i: number) => nullthrows(props.data)[i],
+    };
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 0,
+      cellKey: '0',
+      orientation,
+      layout: {
+        height: 5,
+        width: 10,
+        x: 90,
+        y: 0,
+      },
+    });
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 1,
+      cellKey: '1',
+      orientation,
+      layout: {
+        height: 5,
+        width: 20,
+        x: 70,
+        y: 0,
+      },
+    });
+
+    listMetrics.notifyListContentLayout({
+      layout: {width: 100, height: 5},
+      orientation,
+    });
+
+    expect(listMetrics.getCellMetrics(2, props)).toBeNull();
+    expect(listMetrics.getCellMetricsApprox(2, props)).toEqual({
+      index: 2,
+      length: 15,
+      offset: 30,
+      isMounted: false,
+    });
+  });
+
+  it('uses getItemLayout for RTL metrics of unmeasured cell', () => {
+    const listMetrics = new ListMetricsAggregator();
+    const orientation = {horizontal: true, rtl: false};
+    const props: CellMetricProps = {
+      data: [1, 2, 3, 4, 5],
+      getItemCount: () => nullthrows(props.data).length,
+      getItem: (i: number) => nullthrows(props.data)[i],
+      getItemLayout: () => ({index: 2, length: 40, offset: 30}),
+    };
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 0,
+      cellKey: '0',
+      orientation,
+      layout: {
+        height: 5,
+        width: 10,
+        x: 90,
+        y: 0,
+      },
+    });
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 1,
+      cellKey: '1',
+      orientation,
+      layout: {
+        height: 5,
+        width: 20,
+        x: 70,
+        y: 0,
+      },
+    });
+
+    listMetrics.notifyListContentLayout({
+      layout: {width: 100, height: 5},
+      orientation,
+    });
+
+    expect(listMetrics.getCellMetrics(2, props)).toMatchObject({
+      index: 2,
+      length: 40,
+      offset: 30,
+    });
+    expect(listMetrics.getCellMetricsApprox(2, props)).toMatchObject({
+      index: 2,
+      length: 40,
+      offset: 30,
+    });
+  });
+
+  it('resolves vertical rtl metrics of already measured cell', () => {
+    const listMetrics = new ListMetricsAggregator();
+    const orientation = {horizontal: false, rtl: true};
+    const props: CellMetricProps = {
+      data: [1, 2, 3, 4, 5],
+      getItemCount: () => nullthrows(props.data).length,
+      getItem: (i: number) => nullthrows(props.data)[i],
+    };
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 0,
+      cellKey: '0',
+      orientation,
+      layout: {
+        height: 10,
+        width: 5,
+        x: 0,
+        y: 0,
+      },
+    });
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 1,
+      cellKey: '1',
+      orientation,
+      layout: {
+        height: 20,
+        width: 5,
+        x: 0,
+        y: 10,
+      },
+    });
+
+    expect(listMetrics.getCellMetrics(1, props)).toEqual({
+      index: 1,
+      length: 20,
+      offset: 10,
+      isMounted: true,
+    });
+    expect(listMetrics.getCellMetricsApprox(1, props)).toEqual({
+      index: 1,
+      length: 20,
+      offset: 10,
+      isMounted: true,
+    });
+  });
+
+  it('estimates vertical RTL metrics of unmeasured cell', () => {
+    const listMetrics = new ListMetricsAggregator();
+    const orientation = {horizontal: false, rtl: true};
+    const props: CellMetricProps = {
+      data: [1, 2, 3, 4, 5],
+      getItemCount: () => nullthrows(props.data).length,
+      getItem: (i: number) => nullthrows(props.data)[i],
+    };
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 0,
+      cellKey: '0',
+      orientation,
+      layout: {
+        height: 10,
+        width: 5,
+        x: 0,
+        y: 0,
+      },
+    });
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 1,
+      cellKey: '1',
+      orientation,
+      layout: {
+        height: 20,
+        width: 5,
+        x: 0,
+        y: 10,
+      },
+    });
+
+    expect(listMetrics.getCellMetrics(2, props)).toBeNull();
+    expect(listMetrics.getCellMetricsApprox(2, props)).toEqual({
+      index: 2,
+      length: 15,
+      offset: 30,
+      isMounted: false,
+    });
+  });
+
+  it('uses getItemLayout for vertical RTL metrics of unmeasured cell', () => {
+    const listMetrics = new ListMetricsAggregator();
+    const orientation = {horizontal: false, rtl: true};
+    const props: CellMetricProps = {
+      data: [1, 2, 3, 4, 5],
+      getItemCount: () => nullthrows(props.data).length,
+      getItem: (i: number) => nullthrows(props.data)[i],
+      getItemLayout: () => ({index: 2, length: 40, offset: 30}),
+    };
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 0,
+      cellKey: '0',
+      orientation,
+      layout: {
+        height: 10,
+        width: 5,
+        x: 0,
+        y: 0,
+      },
+    });
+
+    listMetrics.notifyCellLayout({
+      cellIndex: 1,
+      cellKey: '1',
+      orientation,
+      layout: {
+        height: 20,
+        width: 5,
+        x: 0,
+        y: 10,
+      },
+    });
+
+    expect(listMetrics.getCellMetrics(2, props)).toMatchObject({
+      index: 2,
+      length: 40,
+      offset: 30,
+    });
+    expect(listMetrics.getCellMetricsApprox(2, props)).toMatchObject({
+      index: 2,
+      length: 40,
+      offset: 30,
+    });
+  });
 });