diff --git a/src/lib/server/docker-disk-usage-core.ts b/src/lib/server/docker-disk-usage-core.ts
new file mode 100644
index 0000000..28446a7
--- /dev/null
+++ b/src/lib/server/docker-disk-usage-core.ts
@@ -0,0 +1,32 @@
+export interface DockerDiskUsageLike {
+	LayersSize?: unknown;
+	ImageUsage?: {
+		TotalSize?: unknown;
+	} | null;
+	Images?: Array<{
+		Size?: unknown;
+	}> | null;
+}
+
+function asNonNegativeFiniteNumber(value: unknown): number | null {
+	return typeof value === 'number' && Number.isFinite(value) && value >= 0
+		? value
+		: null;
+}
+
+/**
+ * Return Docker's aggregate image disk usage without double-counting shared layers.
+ *
+ * `Images[].Size` is each image's virtual size (shared + unique), so adding those
+ * values overstates disk usage whenever images share layers. Docker exposes the
+ * deduplicated total as `ImageUsage.TotalSize` in the current API and as
+ * `LayersSize` in the legacy response shape.
+ */
+export function getImageDiskUsageTotalSize(
+	diskUsage: DockerDiskUsageLike | null | undefined
+): number | null {
+	const currentTotal = asNonNegativeFiniteNumber(diskUsage?.ImageUsage?.TotalSize);
+	if (currentTotal !== null) return currentTotal;
+
+	return asNonNegativeFiniteNumber(diskUsage?.LayersSize);
+}
diff --git a/src/routes/api/dashboard/stats/+server.ts b/src/routes/api/dashboard/stats/+server.ts
index 62d66b3..c71e6a7 100644
--- a/src/routes/api/dashboard/stats/+server.ts
+++ b/src/routes/api/dashboard/stats/+server.ts
@@ -18,6 +18,7 @@ import {
 } from '$lib/server/docker';
 import { listComposeStacks } from '$lib/server/stacks';
 import { countLivePending } from '$lib/server/pending-updates-core';
+import { getImageDiskUsageTotalSize } from '$lib/server/docker-disk-usage-core';
 import { authorize } from '$lib/server/authorize';
 import { parseLabels } from '$lib/utils/label-colors';
 
@@ -239,9 +240,11 @@ export const GET: RequestHandler = async ({ cookies, url }) => {
 
 				// Process disk usage from /system/df for accurate size data
 				if (diskUsage) {
-					// Images: use Size from /system/df
+					// Images: use Docker's aggregate size so shared layers are counted once
 					envStats.images.total = diskUsage.Images?.length || images.length;
-					envStats.images.totalSize = diskUsage.Images?.reduce((sum: number, img: any) => sum + getValidSize(img.Size), 0) || 0;
+					envStats.images.totalSize = getImageDiskUsageTotalSize(diskUsage)
+						?? diskUsage.Images?.reduce((sum: number, img: any) => sum + getValidSize(img.Size), 0)
+						?? 0;
 
 					// Volumes: use UsageData.Size from /system/df
 					envStats.volumes.total = diskUsage.Volumes?.length || volumes.length;
diff --git a/src/routes/api/dashboard/stats/stream/+server.ts b/src/routes/api/dashboard/stats/stream/+server.ts
index 66e9f52..82ca84a 100644
--- a/src/routes/api/dashboard/stats/stream/+server.ts
+++ b/src/routes/api/dashboard/stats/stream/+server.ts
@@ -26,6 +26,7 @@ import { prefersJSON, sseToJSON } from '$lib/server/sse';
 import type { EnvironmentStats } from '../+server';
 import { parseLabels } from '$lib/utils/label-colors';
 import { isEdgeConnected } from '$lib/server/hawser';
+import { getImageDiskUsageTotalSize } from '$lib/server/docker-disk-usage-core';
 
 
 // Skip disk usage collection (Synology NAS performance fix)
@@ -434,9 +435,11 @@ async function getEnvironmentStatsProgressive(
 			: getCachedDiskUsage(env.id)
 				.then((diskUsage) => {
 					if (diskUsage) {
-						// Update images with disk usage data (more accurate)
+						// Update images with Docker's deduplicated aggregate size
 						envStats.images.total = diskUsage.Images?.length || envStats.images.total;
-						envStats.images.totalSize = diskUsage.Images?.reduce((sum: number, img: any) => sum + getValidSize(img.Size), 0) || envStats.images.totalSize;
+						envStats.images.totalSize = getImageDiskUsageTotalSize(diskUsage)
+							?? diskUsage.Images?.reduce((sum: number, img: any) => sum + getValidSize(img.Size), 0)
+							?? envStats.images.totalSize;
 
 						// Volumes from disk usage
 						envStats.volumes.total = diskUsage.Volumes?.length || 0;
diff --git a/tests/docker-disk-usage-core.test.ts b/tests/docker-disk-usage-core.test.ts
new file mode 100644
index 0000000..da5ddaa
--- /dev/null
+++ b/tests/docker-disk-usage-core.test.ts
@@ -0,0 +1,53 @@
+// @ts-expect-error -- bun:test is a runtime built-in with no types installed
+import { describe, expect, test } from 'bun:test';
+import { getImageDiskUsageTotalSize } from '../src/lib/server/docker-disk-usage-core';
+
+describe('getImageDiskUsageTotalSize', () => {
+	test('uses Docker aggregate size instead of summing virtual image sizes', () => {
+		const diskUsage = {
+			LayersSize: 70_326_328_267,
+			Images: [
+				{ Size: 189_295_958_800 },
+				{ Size: 82_498_083_216 }
+			]
+		};
+
+		expect(getImageDiskUsageTotalSize(diskUsage)).toBe(70_326_328_267);
+	});
+
+	test('prefers the current ImageUsage.TotalSize response field', () => {
+		expect(getImageDiskUsageTotalSize({
+			ImageUsage: { TotalSize: 42 },
+			LayersSize: 99
+		})).toBe(42);
+	});
+
+	test('supports the legacy LayersSize response field', () => {
+		expect(getImageDiskUsageTotalSize({ LayersSize: 42 })).toBe(42);
+	});
+
+	test('preserves zero as a valid aggregate size', () => {
+		expect(getImageDiskUsageTotalSize({
+			ImageUsage: { TotalSize: 0 },
+			LayersSize: 99
+		})).toBe(0);
+		expect(getImageDiskUsageTotalSize({ LayersSize: 0 })).toBe(0);
+	});
+
+	test('falls back from an invalid current value to a valid legacy value', () => {
+		expect(getImageDiskUsageTotalSize({
+			ImageUsage: { TotalSize: Number.NaN },
+			LayersSize: 42
+		})).toBe(42);
+	});
+
+	test('returns null when no trustworthy aggregate is available', () => {
+		expect(getImageDiskUsageTotalSize(undefined)).toBeNull();
+		expect(getImageDiskUsageTotalSize({})).toBeNull();
+		expect(getImageDiskUsageTotalSize({ LayersSize: -1 })).toBeNull();
+		expect(getImageDiskUsageTotalSize({
+			ImageUsage: { TotalSize: '42' },
+			LayersSize: null
+		})).toBeNull();
+	});
+});