diff --git a/src/core/dicomTags.ts b/src/core/dicomTags.ts
index 3a1ee6e0d..7f599f262 100644
--- a/src/core/dicomTags.ts
+++ b/src/core/dicomTags.ts
@@ -33,8 +33,20 @@ const tags: Tag[] = [
   { name: 'RescaleIntercept', tag: '0028|1052' },
   { name: 'RescaleSlope', tag: '0028|1053' },
   { name: 'NumberOfFrames', tag: '0028|0008' },
+  { name: 'SequenceOfUltrasoundRegions', tag: '0018|6011' },
+  { name: 'PhysicalDeltaX', tag: '0018|602c' },
+  { name: 'PhysicalDeltaY', tag: '0018|602e' },
+  { name: 'PhysicalUnitsXDirection', tag: '0018|6024' },
+  { name: 'PhysicalUnitsYDirection', tag: '0018|6026' },
 ];
 
 export const TAG_TO_NAME = new Map(tags.map((t) => [t.tag, t.name]));
 export const NAME_TO_TAG = new Map(tags.map((t) => [t.name, t.tag]));
 export const Tags = Object.fromEntries(tags.map((t) => [t.name, t.tag]));
+
+// Splits an itk-wasm-style "GGGG|EEEE" tag into the numeric [group, element]
+// pair emitted by the streaming DICOM parser.
+export const tagToGroupElement = (tag: string): [number, number] => {
+  const [group, element] = tag.split('|');
+  return [parseInt(group, 16), parseInt(element, 16)];
+};
diff --git a/src/core/streaming/dicom/__tests__/ultrasoundRegion.spec.ts b/src/core/streaming/dicom/__tests__/ultrasoundRegion.spec.ts
new file mode 100644
index 000000000..7bc69bf9b
--- /dev/null
+++ b/src/core/streaming/dicom/__tests__/ultrasoundRegion.spec.ts
@@ -0,0 +1,217 @@
+import { describe, it, expect } from 'vitest';
+import type { DataElement } from '@/src/core/streaming/dicom/dicomParser';
+import {
+  decodeUltrasoundRegion,
+  encodeUltrasoundRegionMeta,
+  getUltrasoundRegionFromMetadata,
+  parseUltrasoundRegionFromBlob,
+  US_REGION_META_KEY,
+  US_UNIT_CENTIMETERS,
+} from '@/src/core/streaming/dicom/ultrasoundRegion';
+
+const u16LE = (v: number) => {
+  const b = new Uint8Array(2);
+  new DataView(b.buffer).setUint16(0, v, true);
+  return b;
+};
+
+const f64LE = (v: number) => {
+  const b = new Uint8Array(8);
+  new DataView(b.buffer).setFloat64(0, v, true);
+  return b;
+};
+
+const concat = (parts: Uint8Array[]) => {
+  const total = parts.reduce((sum, p) => sum + p.length, 0);
+  const out = new Uint8Array(total);
+  let offset = 0;
+  parts.forEach((p) => {
+    out.set(p, offset);
+    offset += p.length;
+  });
+  return out;
+};
+
+// Builds an explicit-VR-LE data element for a VR with 2-byte length (US/FD/UI/etc).
+const shortVRElement = (
+  group: number,
+  element: number,
+  vr: string,
+  value: Uint8Array
+) => {
+  const header = new Uint8Array(8);
+  const dv = new DataView(header.buffer);
+  dv.setUint16(0, group, true);
+  dv.setUint16(2, element, true);
+  header[4] = vr.charCodeAt(0);
+  header[5] = vr.charCodeAt(1);
+  dv.setUint16(6, value.length, true);
+  return concat([header, value]);
+};
+
+type Item = { group: number; element: number; vr: string; value: Uint8Array };
+
+// Fake parsed sequence data mirroring what readSequenceValue emits.
+const fakeSequenceData = (items: Item[][]): DataElement['data'] =>
+  items.map(
+    (elements) =>
+      elements.map((e) => ({
+        group: e.group,
+        element: e.element,
+        vr: e.vr,
+        length: e.value.length,
+        data: e.value,
+      })) as DataElement[]
+  );
+
+const wellFormedItem: Item[] = [
+  { group: 0x0018, element: 0x6024, vr: 'US', value: u16LE(US_UNIT_CENTIMETERS) },
+  { group: 0x0018, element: 0x6026, vr: 'US', value: u16LE(US_UNIT_CENTIMETERS) },
+  { group: 0x0018, element: 0x602c, vr: 'FD', value: f64LE(0.05) },
+  { group: 0x0018, element: 0x602e, vr: 'FD', value: f64LE(0.1) },
+];
+
+describe('decodeUltrasoundRegion', () => {
+  it('decodes the first item of the sequence', () => {
+    const region = decodeUltrasoundRegion(fakeSequenceData([wellFormedItem]));
+    expect(region).toEqual({
+      physicalDeltaX: 0.05,
+      physicalDeltaY: 0.1,
+      physicalUnitsXDirection: US_UNIT_CENTIMETERS,
+      physicalUnitsYDirection: US_UNIT_CENTIMETERS,
+    });
+  });
+
+  it('returns null when the sequence is empty', () => {
+    expect(decodeUltrasoundRegion([])).toBeNull();
+  });
+
+  it('returns null when the data is not a sequence', () => {
+    expect(decodeUltrasoundRegion(undefined)).toBeNull();
+    expect(decodeUltrasoundRegion(new Uint8Array(4))).toBeNull();
+  });
+
+  it('returns null when a required field is missing', () => {
+    const missingDeltaY = wellFormedItem.filter(
+      (e) => !(e.group === 0x0018 && e.element === 0x602e)
+    );
+    expect(decodeUltrasoundRegion(fakeSequenceData([missingDeltaY]))).toBeNull();
+  });
+
+  it('ignores items beyond the first', () => {
+    const second: Item[] = [
+      { group: 0x0018, element: 0x6024, vr: 'US', value: u16LE(0) },
+      { group: 0x0018, element: 0x6026, vr: 'US', value: u16LE(0) },
+      { group: 0x0018, element: 0x602c, vr: 'FD', value: f64LE(999) },
+      { group: 0x0018, element: 0x602e, vr: 'FD', value: f64LE(999) },
+    ];
+    const region = decodeUltrasoundRegion(
+      fakeSequenceData([wellFormedItem, second])
+    );
+    expect(region?.physicalDeltaX).toBe(0.05);
+  });
+});
+
+describe('encodeUltrasoundRegionMeta / getUltrasoundRegionFromMetadata', () => {
+  it('round-trips through the metadata tag array', () => {
+    const region = {
+      physicalDeltaX: 0.05,
+      physicalDeltaY: 0.1,
+      physicalUnitsXDirection: US_UNIT_CENTIMETERS,
+      physicalUnitsYDirection: US_UNIT_CENTIMETERS,
+    };
+    const entry = encodeUltrasoundRegionMeta(region);
+    expect(entry[0]).toBe(US_REGION_META_KEY);
+
+    const meta: Array<[string, string]> = [
+      ['0008|0060', 'US'],
+      entry,
+      ['0010|0010', 'PATIENT^NAME'],
+    ];
+    expect(getUltrasoundRegionFromMetadata(meta)).toEqual(region);
+  });
+
+  it('returns null when the entry is absent', () => {
+    expect(getUltrasoundRegionFromMetadata([])).toBeNull();
+    expect(getUltrasoundRegionFromMetadata(null)).toBeNull();
+    expect(getUltrasoundRegionFromMetadata(undefined)).toBeNull();
+  });
+
+  it('returns null when the entry value is unparseable', () => {
+    expect(
+      getUltrasoundRegionFromMetadata([[US_REGION_META_KEY, 'not-json']])
+    ).toBeNull();
+  });
+});
+
+// Builds a minimal DICOM P10 byte stream containing only what the ultrasound
+// parser needs: preamble, DICM magic, a TransferSyntaxUID (Explicit VR LE),
+// and a SequenceOfUltrasoundRegions with one populated item.
+const buildDicomBlob = (item: Item[]) => {
+  const preamble = new Uint8Array(128);
+  const magic = new TextEncoder().encode('DICM');
+
+  // File Meta Info: just TransferSyntaxUID. The parser exits the meta block
+  // as soon as it peeks a non-0x0002 group, so FileMetaInformationGroupLength
+  // is not required here.
+  const tsxValue = new TextEncoder().encode('1.2.840.10008.1.2.1\0');
+  const tsx = shortVRElement(0x0002, 0x0010, 'UI', tsxValue);
+
+  const itemBody = concat(
+    item.map((e) => shortVRElement(e.group, e.element, e.vr, e.value))
+  );
+
+  // Item header: (fffe,e000) tag + 4-byte length.
+  const itemHeader = new Uint8Array(8);
+  const ivh = new DataView(itemHeader.buffer);
+  ivh.setUint16(0, 0xfffe, true);
+  ivh.setUint16(2, 0xe000, true);
+  ivh.setUint32(4, itemBody.length, true);
+
+  const sequenceBody = concat([itemHeader, itemBody]);
+
+  // SQ header: tag + "SQ" + 2 reserved + 4-byte length.
+  const sqHeader = new Uint8Array(12);
+  const sqh = new DataView(sqHeader.buffer);
+  sqh.setUint16(0, 0x0018, true);
+  sqh.setUint16(2, 0x6011, true);
+  sqHeader[4] = 'S'.charCodeAt(0);
+  sqHeader[5] = 'Q'.charCodeAt(0);
+  sqh.setUint32(8, sequenceBody.length, true);
+
+  // Pixel data tag so the parser reaches its stop condition cleanly.
+  const pixelDataTag = new Uint8Array(4);
+  new DataView(pixelDataTag.buffer).setUint16(0, 0x7fe0, true);
+  new DataView(pixelDataTag.buffer).setUint16(2, 0x0010, true);
+
+  return new Blob([
+    concat([preamble, magic, tsx, sqHeader, sequenceBody, pixelDataTag]),
+  ]);
+};
+
+describe('parseUltrasoundRegionFromBlob', () => {
+  it('extracts the region from a synthetic DICOM blob', async () => {
+    const blob = buildDicomBlob(wellFormedItem);
+    const region = await parseUltrasoundRegionFromBlob(blob);
+    expect(region).toEqual({
+      physicalDeltaX: 0.05,
+      physicalDeltaY: 0.1,
+      physicalUnitsXDirection: US_UNIT_CENTIMETERS,
+      physicalUnitsYDirection: US_UNIT_CENTIMETERS,
+    });
+  });
+
+  it('returns null when the blob has no SequenceOfUltrasoundRegions', async () => {
+    // Build a blob with only the TransferSyntaxUID + pixel data tag.
+    const preamble = new Uint8Array(128);
+    const magic = new TextEncoder().encode('DICM');
+    const tsxValue = new TextEncoder().encode('1.2.840.10008.1.2.1\0');
+    const tsx = shortVRElement(0x0002, 0x0010, 'UI', tsxValue);
+    const pixelDataTag = new Uint8Array(4);
+    new DataView(pixelDataTag.buffer).setUint16(0, 0x7fe0, true);
+    new DataView(pixelDataTag.buffer).setUint16(2, 0x0010, true);
+    const blob = new Blob([concat([preamble, magic, tsx, pixelDataTag])]);
+
+    expect(await parseUltrasoundRegionFromBlob(blob)).toBeNull();
+  });
+});
diff --git a/src/core/streaming/dicom/dicomFileMetaLoader.ts b/src/core/streaming/dicom/dicomFileMetaLoader.ts
index ec6adab43..581a67947 100644
--- a/src/core/streaming/dicom/dicomFileMetaLoader.ts
+++ b/src/core/streaming/dicom/dicomFileMetaLoader.ts
@@ -1,6 +1,11 @@
 import { ReadDicomTagsFunction } from '@/src/core/streaming/dicom/dicomMetaLoader';
 import { MetaLoader } from '@/src/core/streaming/types';
 import { Maybe } from '@/src/types';
+import { Tags } from '@/src/core/dicomTags';
+import {
+  encodeUltrasoundRegionMeta,
+  parseUltrasoundRegionFromBlob,
+} from '@/src/core/streaming/dicom/ultrasoundRegion';
 
 export class DicomFileMetaLoader implements MetaLoader {
   public tags: Maybe<Array<[string, string]>>;
@@ -24,6 +29,14 @@ export class DicomFileMetaLoader implements MetaLoader {
   async load() {
     if (this.tags) return;
     this.tags = await this.readDicomTags(this.file);
+
+    const modality = new Map(this.tags).get(Tags.Modality)?.trim();
+    if (modality === 'US') {
+      const region = await parseUltrasoundRegionFromBlob(this.file);
+      if (region) {
+        this.tags.push(encodeUltrasoundRegionMeta(region));
+      }
+    }
   }
 
   stop() {
diff --git a/src/core/streaming/dicom/dicomMetaLoader.ts b/src/core/streaming/dicom/dicomMetaLoader.ts
index 2be42d2c1..81727f11c 100644
--- a/src/core/streaming/dicom/dicomMetaLoader.ts
+++ b/src/core/streaming/dicom/dicomMetaLoader.ts
@@ -9,6 +9,12 @@ import { Awaitable } from '@vueuse/core';
 import { toAscii } from '@/src/utils';
 import { FILE_EXT_TO_MIME } from '@/src/io/mimeTypes';
 import { Tags } from '@/src/core/dicomTags';
+import {
+  decodeUltrasoundRegion,
+  encodeUltrasoundRegionMeta,
+  SEQUENCE_OF_ULTRASOUND_REGIONS,
+  UltrasoundRegion,
+} from '@/src/core/streaming/dicom/ultrasoundRegion';
 
 export type ReadDicomTagsFunction = (
   file: File
@@ -51,6 +57,7 @@ export class DicomMetaLoader implements MetaLoader {
     let explicitVr = true;
     let dicomUpToPixelDataIdx = -1;
     let modality: string | undefined;
+    let ultrasoundRegion: UltrasoundRegion | null = null;
 
     const parse = createDicomParser({
       stopAtElement(group, element) {
@@ -66,6 +73,13 @@ export class DicomMetaLoader implements MetaLoader {
         if (el.group === 0x0008 && el.element === 0x0060 && el.data) {
           modality = toAscii(el.data as Uint8Array).trim();
         }
+        if (
+          el.group === SEQUENCE_OF_ULTRASOUND_REGIONS[0] &&
+          el.element === SEQUENCE_OF_ULTRASOUND_REGIONS[1] &&
+          !ultrasoundRegion
+        ) {
+          ultrasoundRegion = decodeUltrasoundRegion(el.data);
+        }
       },
     });
 
@@ -115,6 +129,10 @@ export class DicomMetaLoader implements MetaLoader {
 
     const metadataFile = new File([validPixelDataBlob], 'file.dcm');
     this.tags = await this.readDicomTags(metadataFile);
+
+    if (modality === 'US' && ultrasoundRegion) {
+      this.tags.push(encodeUltrasoundRegionMeta(ultrasoundRegion));
+    }
   }
 
   stop() {
diff --git a/src/core/streaming/dicom/ultrasoundRegion.ts b/src/core/streaming/dicom/ultrasoundRegion.ts
new file mode 100644
index 000000000..d57bf1b4b
--- /dev/null
+++ b/src/core/streaming/dicom/ultrasoundRegion.ts
@@ -0,0 +1,135 @@
+import {
+  createDicomParser,
+  DataElement,
+} from '@/src/core/streaming/dicom/dicomParser';
+import { Tags, tagToGroupElement } from '@/src/core/dicomTags';
+
+export const US_REGION_META_KEY = '__volview_us_region';
+
+// DICOM unit codes for PhysicalUnitsXDirection / YDirection
+// 0x0003 = centimeters. See DICOM PS3.3 C.8.5.5.1.1.
+export const US_UNIT_CENTIMETERS = 3;
+
+export type UltrasoundRegion = {
+  physicalDeltaX: number;
+  physicalDeltaY: number;
+  physicalUnitsXDirection: number;
+  physicalUnitsYDirection: number;
+};
+
+export const SEQUENCE_OF_ULTRASOUND_REGIONS = tagToGroupElement(
+  Tags.SequenceOfUltrasoundRegions
+);
+const PHYSICAL_DELTA_X = tagToGroupElement(Tags.PhysicalDeltaX);
+const PHYSICAL_DELTA_Y = tagToGroupElement(Tags.PhysicalDeltaY);
+const PHYSICAL_UNITS_X_DIRECTION = tagToGroupElement(
+  Tags.PhysicalUnitsXDirection
+);
+const PHYSICAL_UNITS_Y_DIRECTION = tagToGroupElement(
+  Tags.PhysicalUnitsYDirection
+);
+
+const isTag = (el: DataElement, [group, element]: [number, number]) =>
+  el.group === group && el.element === element;
+
+const readFloat64LE = (bytes: Uint8Array) =>
+  new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength).getFloat64(
+    0,
+    true
+  );
+
+const readUint16LE = (bytes: Uint8Array) =>
+  new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength).getUint16(
+    0,
+    true
+  );
+
+/**
+ * Decodes the first item of a SequenceOfUltrasoundRegions element.
+ * Returns null if required fields are missing.
+ */
+export function decodeUltrasoundRegion(
+  sequenceData: DataElement['data']
+): UltrasoundRegion | null {
+  if (!Array.isArray(sequenceData) || sequenceData.length === 0) return null;
+  const [firstItem] = sequenceData;
+
+  const findBytes = (target: [number, number]) => {
+    const el = firstItem.find((inner) => isTag(inner, target));
+    if (!el || !(el.data instanceof Uint8Array)) return null;
+    return el.data;
+  };
+
+  const deltaXBytes = findBytes(PHYSICAL_DELTA_X);
+  const deltaYBytes = findBytes(PHYSICAL_DELTA_Y);
+  const unitsXBytes = findBytes(PHYSICAL_UNITS_X_DIRECTION);
+  const unitsYBytes = findBytes(PHYSICAL_UNITS_Y_DIRECTION);
+
+  if (!deltaXBytes || !deltaYBytes || !unitsXBytes || !unitsYBytes) {
+    return null;
+  }
+
+  return {
+    physicalDeltaX: readFloat64LE(deltaXBytes),
+    physicalDeltaY: readFloat64LE(deltaYBytes),
+    physicalUnitsXDirection: readUint16LE(unitsXBytes),
+    physicalUnitsYDirection: readUint16LE(unitsYBytes),
+  };
+}
+
+/**
+ * Parses a DICOM blob and returns the first ultrasound region, if present.
+ */
+export async function parseUltrasoundRegionFromBlob(
+  blob: Blob
+): Promise<UltrasoundRegion | null> {
+  let region: UltrasoundRegion | null = null;
+
+  const parse = createDicomParser({
+    stopAtElement(group, element) {
+      return group === 0x7fe0 && element === 0x0010;
+    },
+    onDataElement(el) {
+      if (region) return;
+      if (isTag(el, SEQUENCE_OF_ULTRASOUND_REGIONS)) {
+        region = decodeUltrasoundRegion(el.data);
+      }
+    },
+  });
+
+  const stream = blob.stream();
+  const reader = stream.getReader();
+  try {
+    while (!region) {
+      const { value, done } = await reader.read();
+      if (done) break;
+      const result = parse(value);
+      if (result.done) break;
+    }
+  } catch {
+    return null;
+  } finally {
+    reader.releaseLock();
+  }
+
+  return region;
+}
+
+export function encodeUltrasoundRegionMeta(
+  region: UltrasoundRegion
+): [string, string] {
+  return [US_REGION_META_KEY, JSON.stringify(region)];
+}
+
+export function getUltrasoundRegionFromMetadata(
+  meta: ReadonlyArray<readonly [string, string]> | null | undefined
+): UltrasoundRegion | null {
+  if (!meta) return null;
+  const entry = meta.find(([key]) => key === US_REGION_META_KEY);
+  if (!entry) return null;
+  try {
+    return JSON.parse(entry[1]) as UltrasoundRegion;
+  } catch {
+    return null;
+  }
+}
diff --git a/src/core/streaming/dicomChunkImage.ts b/src/core/streaming/dicomChunkImage.ts
index 2e9904b65..d6e1feeeb 100644
--- a/src/core/streaming/dicomChunkImage.ts
+++ b/src/core/streaming/dicomChunkImage.ts
@@ -26,6 +26,10 @@ import {
 import { ensureError } from '@/src/utils';
 import { computed } from 'vue';
 import vtkITKHelper from '@kitware/vtk.js/Common/DataModel/ITKHelper';
+import {
+  getUltrasoundRegionFromMetadata,
+  US_UNIT_CENTIMETERS,
+} from '@/src/core/streaming/dicom/ultrasoundRegion';
 
 const { fastComputeRange } = vtkDataArray;
 
@@ -279,6 +283,28 @@ export default class DicomChunkImage
   private reallocateImage() {
     this.vtkImageData.value.delete();
     this.vtkImageData.value = allocateImageFromChunks(this.chunks);
+    this.applyUltrasoundSpacing();
+  }
+
+  private applyUltrasoundSpacing() {
+    if (this.getModality() !== 'US') return;
+
+    const region = getUltrasoundRegionFromMetadata(this.getDicomMetadata());
+    if (!region) return;
+    if (
+      region.physicalUnitsXDirection !== US_UNIT_CENTIMETERS ||
+      region.physicalUnitsYDirection !== US_UNIT_CENTIMETERS
+    ) {
+      return;
+    }
+
+    const CM_TO_MM = 10;
+    const [, , zSpacing] = this.vtkImageData.value.getSpacing();
+    this.vtkImageData.value.setSpacing([
+      region.physicalDeltaX * CM_TO_MM,
+      region.physicalDeltaY * CM_TO_MM,
+      zSpacing,
+    ]);
   }
 
   private updateDataRangeFromChunks() {
diff --git a/tests/specs/configTestUtils.ts b/tests/specs/configTestUtils.ts
index 0fff6a9cd..6e045dfb2 100644
--- a/tests/specs/configTestUtils.ts
+++ b/tests/specs/configTestUtils.ts
@@ -73,6 +73,14 @@ export const FETUS_DATASET = {
   name: 'fetus.zip',
 } as const;
 
+// Multiframe ultrasound DICOM from pydicom public test data.
+// SequenceOfUltrasoundRegions: PhysicalDeltaX/Y = 0.05104970559 cm/pixel
+// (unit code 3 = cm), so with US spacing fix the VTK spacing is ~0.5105 mm.
+export const US_MULTIFRAME_DICOM = {
+  url: 'https://data.kitware.com/api/v1/file/69e1630646ef98a20f563020/download',
+  name: 'US_multiframe_30frames.dcm',
+} as const;
+
 export type DatasetResource = {
   url: string;
   name?: string;
diff --git a/tests/specs/ultrasound-spacing.e2e.ts b/tests/specs/ultrasound-spacing.e2e.ts
new file mode 100644
index 000000000..e48f84b3a
--- /dev/null
+++ b/tests/specs/ultrasound-spacing.e2e.ts
@@ -0,0 +1,92 @@
+import { US_MULTIFRAME_DICOM } from './configTestUtils';
+import { openUrls } from './utils';
+import { volViewPage } from '../pageobjects/volview.page';
+
+const clickAt = async (x: number, y: number) => {
+  await browser
+    .action('pointer')
+    .move({ x: Math.round(x), y: Math.round(y) })
+    .down()
+    .up()
+    .perform();
+};
+
+// Offset between the two ruler clicks (in canvas pixels).
+// The measured ruler length in mm depends on this offset, the canvas size,
+// and the image spacing. With the US spacing fix the VTK spacing comes from
+// SequenceOfUltrasoundRegions (~0.5105 mm); without the fix it falls back to
+// 1.0 mm, which makes the measured length ~1.96x larger.
+const CLICK_DX = 0;
+const CLICK_DY = 100;
+
+// Calibrated length (mm) that the ruler reports when the US spacing fix is
+// active. Obtained by running this test once with the fix enabled.
+// Without the fix the VTK spacing falls back to 1.0 mm/pixel, which makes
+// the measured length grow to ~97 mm (~1.96x) and this assertion fails.
+const EXPECTED_LENGTH_MM = 49.35;
+const LENGTH_TOLERANCE_MM = 1.5;
+
+describe('Ultrasound image spacing', () => {
+  it('ruler length reflects physical spacing from SequenceOfUltrasoundRegions', async () => {
+    await openUrls([US_MULTIFRAME_DICOM]);
+
+    // Activate the ruler tool
+    const rulerBtn = await $('button span i[class~=mdi-ruler]');
+    await rulerBtn.waitForClickable();
+    await rulerBtn.click();
+
+    // Place the ruler on the first view's canvas
+    const views = await volViewPage.views;
+    const canvas = views[0];
+    const loc = await canvas.getLocation();
+    const size = await canvas.getSize();
+    const cx = loc.x + size.width / 2;
+    const cy = loc.y + size.height / 2;
+
+    await clickAt(cx - CLICK_DX / 2, cy - CLICK_DY / 2);
+    await clickAt(cx + CLICK_DX / 2, cy + CLICK_DY / 2);
+
+    // Open Annotations > Measurements to read the ruler length
+    const annotationsTab = await $(
+      'button[data-testid="module-tab-Annotations"]'
+    );
+    await annotationsTab.click();
+
+    const measurementsTab = await $('button.v-tab*=Measurements');
+    await measurementsTab.waitForClickable();
+    await measurementsTab.click();
+
+    // The ruler details panel renders `{value}mm`; read the first length.
+    let lengthMm = 0;
+    await browser.waitUntil(
+      async () => {
+        const spans = await $$('.v-list-item .value');
+        for (const span of spans) {
+          const text = await span.getText();
+          const match = text.match(/([\d.]+)\s*mm/);
+          if (match) {
+            lengthMm = parseFloat(match[1]);
+            return lengthMm > 0;
+          }
+        }
+        return false;
+      },
+      {
+        timeout: 10_000,
+        timeoutMsg: 'Ruler length (mm) not found in measurements sidebar',
+      }
+    );
+
+    console.log(`[ultrasound-spacing] measured ruler length: ${lengthMm} mm`);
+
+    if (EXPECTED_LENGTH_MM > 0) {
+      expect(lengthMm).toBeGreaterThan(
+        EXPECTED_LENGTH_MM - LENGTH_TOLERANCE_MM
+      );
+      expect(lengthMm).toBeLessThan(EXPECTED_LENGTH_MM + LENGTH_TOLERANCE_MM);
+    } else {
+      // Calibration mode: any positive value passes, actual number is logged.
+      expect(lengthMm).toBeGreaterThan(0);
+    }
+  });
+});