diff --git a/src/components/flame-graph/Canvas.tsx b/src/components/flame-graph/Canvas.tsx
index c7b042fa0f..caf03dd00a 100644
--- a/src/components/flame-graph/Canvas.tsx
+++ b/src/components/flame-graph/Canvas.tsx
@@ -419,10 +419,10 @@ class FlameGraphCanvasImpl extends React.PureComponent<Props> {
       return null;
     }
 
-    const ratio =
-      stackTiming.end[flameGraphTimingIndex] -
-      stackTiming.start[flameGraphTimingIndex];
-
+    const ratio = flameGraphTiming.getRatioOfRootTotalSummary(
+      depth,
+      flameGraphTimingIndex
+    );
     let percentage = formatPercent(ratio);
     if (tracedTiming) {
       const { total } = getSelfAndTotalForCallNode(
diff --git a/src/profile-logic/call-tree.ts b/src/profile-logic/call-tree.ts
index f870e0f703..0bd8f5ece6 100644
--- a/src/profile-logic/call-tree.ts
+++ b/src/profile-logic/call-tree.ts
@@ -51,6 +51,7 @@ export type CallTreeTimingsNonInverted = {
   self: Float64Array;
   total: Float64Array;
   rootTotalSummary: number; // sum of absolute values, this is used for computing percentages
+  flameGraphWidthTotal: number; // used as 100% reference for flame graph box widths
 };
 
 type TotalAndHasChildren = { total: number; hasChildren: boolean };
@@ -723,7 +724,11 @@ export function computeCallNodeSelfAndSummary(
     rootTotalSummary += abs(callNodeSelf[callNodeIndex]);
   }
 
-  return { callNodeSelf, rootTotalSummary };
+  return {
+    callNodeSelf,
+    rootTotalSummary,
+    flameGraphWidthTotal: rootTotalSummary,
+  };
 }
 
 export function getSelfAndTotalForCallNode(
@@ -894,7 +899,8 @@ export function computeCallTreeTimingsNonInverted(
   callNodeSelfAndSummary: CallNodeSelfAndSummary
 ): CallTreeTimingsNonInverted {
   const callNodeTable = callNodeInfo.getCallNodeTable();
-  const { callNodeSelf, rootTotalSummary } = callNodeSelfAndSummary;
+  const { callNodeSelf, rootTotalSummary, flameGraphWidthTotal } =
+    callNodeSelfAndSummary;
 
   // Compute the following variables:
   const callNodeTotal = new Float64Array(callNodeTable.length);
@@ -932,6 +938,7 @@ export function computeCallTreeTimingsNonInverted(
     total: callNodeTotal,
     callNodeHasChildren,
     rootTotalSummary,
+    flameGraphWidthTotal,
   };
 }
 
@@ -1334,5 +1341,9 @@ export function computeCallNodeTracedSelfAndSummary(
     }
   }
 
-  return { callNodeSelf, rootTotalSummary };
+  return {
+    callNodeSelf,
+    rootTotalSummary,
+    flameGraphWidthTotal: rootTotalSummary,
+  };
 }
diff --git a/src/profile-logic/flame-graph.ts b/src/profile-logic/flame-graph.ts
index 24f8347c5a..a25b674804 100644
--- a/src/profile-logic/flame-graph.ts
+++ b/src/profile-logic/flame-graph.ts
@@ -52,6 +52,25 @@ export interface FlameGraphTiming {
   readonly rowCount: number;
   getRow(depth: number): FlameGraphTimingRow;
   getAllRowsForTesting(): FlameGraphTimingRow[];
+
+  // For a given node / "box", get the sample percentage (as a fraction of 1)
+  // that should be displayed in the tooltip for this node.
+  getRatioOfRootTotalSummary(depth: number, indexInRow: number): number;
+}
+
+// Returns the width of a box as a fraction of the full flame graph width.
+function _getBoxWidth(
+  flameGraphTiming: FlameGraphTiming,
+  depth: number,
+  indexInRow: number
+): number {
+  const row = flameGraphTiming.getRow(depth);
+  if (indexInRow < 0 || indexInRow >= row.length) {
+    throw new Error(
+      `Out-of-bounds call to getRatioOfRootTotalSummary: For depth ${depth}, ${indexInRow} is outside 0..${row.length}`
+    );
+  }
+  return row.end[indexInRow] - row.start[indexInRow];
 }
 
 class FlameGraphTimingNonInverted implements FlameGraphTiming {
@@ -104,8 +123,16 @@ class FlameGraphTimingNonInverted implements FlameGraphTiming {
     return rows;
   }
 
+  // For a given node / "box", get the sample percentage (as a fraction of 1) that
+  // should be displayed in the tooltip for this node.
+  getRatioOfRootTotalSummary(depth: number, indexInRow: number): number {
+    const ratioOfFullWidth = _getBoxWidth(this, depth, indexInRow);
+    const total = ratioOfFullWidth * this._callTreeTimings.flameGraphWidthTotal;
+    return total / this._callTreeTimings.rootTotalSummary;
+  }
+
   _buildNextTimingRow(): void {
-    const { total, self, rootTotalSummary } = this._callTreeTimings;
+    const { total, self, flameGraphWidthTotal } = this._callTreeTimings;
     const { prefix } = this._callNodeTable;
 
     const depth = this._timingRows.length;
@@ -142,8 +169,8 @@ class FlameGraphTimingNonInverted implements FlameGraphTiming {
       }
       startPerCallNode[nodeIndex] = currentStart;
 
-      const totalRelative = abs(totalVal / rootTotalSummary);
-      const selfRelativeVal = abs(self[nodeIndex] / rootTotalSummary);
+      const totalRelative = abs(totalVal / flameGraphWidthTotal);
+      const selfRelativeVal = abs(self[nodeIndex] / flameGraphWidthTotal);
 
       const currentEnd = currentStart + totalRelative;
       start.push(currentStart);
@@ -435,6 +462,14 @@ class FlameGraphTimingInverted implements FlameGraphTiming {
     return rows;
   }
 
+  // For a given node / "box", get the sample percentage (as a fraction of 1) that
+  // should be displayed in the tooltip for this node. In the inverted flame
+  // graph, box widths are computed relative to rootTotalSummary, so the box
+  // width is already the ratio we want.
+  getRatioOfRootTotalSummary(depth: number, indexInRow: number): number {
+    return _getBoxWidth(this, depth, indexInRow);
+  }
+
   _compareCallNodesByFuncName = (
     a: IndexIntoCallNodeTable,
     b: IndexIntoCallNodeTable
diff --git a/src/test/store/__snapshots__/profile-view.test.ts.snap b/src/test/store/__snapshots__/profile-view.test.ts.snap
index 702b836990..8ae46ca333 100644
--- a/src/test/store/__snapshots__/profile-view.test.ts.snap
+++ b/src/test/store/__snapshots__/profile-view.test.ts.snap
@@ -2362,6 +2362,7 @@ CallTree {
         0,
         0,
       ],
+      "flameGraphWidthTotal": 2,
       "rootTotalSummary": 2,
       "self": Float64Array [
         0,
diff --git a/src/test/unit/profile-tree.test.ts b/src/test/unit/profile-tree.test.ts
index 48c82e95e1..d535aadd59 100644
--- a/src/test/unit/profile-tree.test.ts
+++ b/src/test/unit/profile-tree.test.ts
@@ -86,6 +86,7 @@ describe('unfiltered call tree', function () {
         type: 'NON_INVERTED',
         timings: {
           rootTotalSummary: 3,
+          flameGraphWidthTotal: 3,
           callNodeHasChildren: new Uint8Array([1, 1, 1, 1, 0, 1, 0, 1, 0]),
           self: new Float64Array([0, 0, 0, 0, 1, 0, 1, 0, 1]),
           total: new Float64Array([3, 3, 2, 1, 1, 1, 1, 1, 1]),
diff --git a/src/types/profile-derived.ts b/src/types/profile-derived.ts
index 10fbae4239..6d7b2fc41f 100644
--- a/src/types/profile-derived.ts
+++ b/src/types/profile-derived.ts
@@ -877,6 +877,12 @@ export type CallNodeSelfAndSummary = {
   // The sum of absolute values in callNodeSelf.
   // This is used for computing the percentages displayed in the call tree.
   rootTotalSummary: number;
+  // The total used as the 100% reference for flame graph box widths.
+  // Usually equals rootTotalSummary, but for the upper wing it is set to the
+  // total of samples that contain the selected function, so that the root node
+  // fills the full flame graph width while percentages remain relative to all
+  // filtered samples.
+  flameGraphWidthTotal: number;
 };
 
 /**