diff --git a/src/annotation/index.ts b/src/annotation/index.ts
index db2dded24..fcd261743 100644
--- a/src/annotation/index.ts
+++ b/src/annotation/index.ts
@@ -54,7 +54,9 @@ import {
 import { parseDataTypeValue } from "#src/util/lerp.js";
 import { getRandomHexString } from "#src/util/random.js";
 import { NullarySignal, Signal } from "#src/util/signal.js";
+import { formatLength } from "#src/util/spatial_units.js";
 import { Uint64 } from "#src/util/uint64.js";
+import { ALLOWED_UNITS } from "#src/widget/scale_bar.js";
 
 export type AnnotationId = string;
 
@@ -106,6 +108,7 @@ export interface AnnotationNumericPropertySpec
   min?: number;
   max?: number;
   step?: number;
+  format?: (x: number) => string;
 }
 
 export const propertyTypeDataType: Record<
@@ -496,6 +499,9 @@ export function formatNumericProperty(
   property: AnnotationNumericPropertySpec,
   value: number,
 ): string {
+  if (property.format) {
+    return property.format(value);
+  }
   const formattedValue =
     property.type === "float32" ? value.toPrecision(6) : value.toString();
   const { enumValues, enumLabels } = property;
@@ -695,6 +701,15 @@ export interface AnnotationTypeHandler<T extends Annotation = Annotation> {
     annotation: T,
     callback: (vec: Float32Array, isVector: boolean) => void,
   ) => void;
+  defaultProperties: (
+    annotation: T,
+    layerPosition: Float32Array<ArrayBufferLike>[],
+    scales: Float64Array,
+    units: readonly string[],
+  ) => {
+    properties: AnnotationNumericPropertySpec[];
+    values: number[];
+  };
 }
 
 function serializeFloatVector(
@@ -751,6 +766,32 @@ function deserializeTwoFloatVectors(
   return offset;
 }
 
+function lineLength(
+  annotationLayerPositions: Float32Array<ArrayBufferLike>[],
+  scales: Float64Array,
+  units: readonly string[],
+) {
+  if (annotationLayerPositions.length !== 2) {
+    return;
+  }
+  const [pointA, pointB] = annotationLayerPositions;
+  const scalesRank = scales.length;
+  const lineRank = pointA.length;
+  if (scalesRank < lineRank) {
+    return;
+  }
+  let lengthSquared = 0;
+  for (let dim = 0; dim < lineRank; dim++) {
+    const unitInfo = ALLOWED_UNITS.find((x) => x.unit === units[dim]);
+    if (!unitInfo) {
+      return;
+    }
+    const voxelToNanometers = scales[dim] * unitInfo.lengthInNanometers;
+    lengthSquared += ((pointA[dim] - pointB[dim]) * voxelToNanometers) ** 2;
+  }
+  return Math.sqrt(lengthSquared);
+}
+
 export const annotationTypeHandlers: Record<
   AnnotationType,
   AnnotationTypeHandler
@@ -814,6 +855,28 @@ export const annotationTypeHandlers: Record<
       callback(annotation.pointA, false);
       callback(annotation.pointB, false);
     },
+    defaultProperties(
+      annotation: Line,
+      annotationLayerPositions: Float32Array<ArrayBufferLike>[],
+      scales: Float64Array,
+      units: readonly string[],
+    ) {
+      annotation;
+      const properties: AnnotationNumericPropertySpec[] = [];
+      const values: number[] = [];
+      const length = lineLength(annotationLayerPositions, scales, units);
+      if (length) {
+        properties.push({
+          type: "float32",
+          identifier: "Length",
+          default: 0,
+          description: "Length of the line annotation in nanometers",
+          format: formatLength,
+        });
+        values.push(length);
+      }
+      return { properties, values };
+    },
   },
   [AnnotationType.POINT]: {
     icon: "⚬",
@@ -858,6 +921,18 @@ export const annotationTypeHandlers: Record<
     visitGeometry(annotation: Point, callback) {
       callback(annotation.point, false);
     },
+    defaultProperties(
+      annotation: Point,
+      layerPosition: Float32Array<ArrayBufferLike>[],
+      scales: Float64Array,
+      units: string[],
+    ) {
+      annotation;
+      layerPosition;
+      scales;
+      units;
+      return { properties: [], values: [] };
+    },
   },
   [AnnotationType.AXIS_ALIGNED_BOUNDING_BOX]: {
     icon: "❑",
@@ -926,6 +1001,18 @@ export const annotationTypeHandlers: Record<
       callback(annotation.pointA, false);
       callback(annotation.pointB, false);
     },
+    defaultProperties(
+      annotation: AxisAlignedBoundingBox,
+      layerPosition: Float32Array<ArrayBufferLike>[],
+      scales: Float64Array,
+      units: string[],
+    ) {
+      annotation;
+      layerPosition;
+      scales;
+      units;
+      return { properties: [], values: [] };
+    },
   },
   [AnnotationType.ELLIPSOID]: {
     icon: "◎",
@@ -994,6 +1081,18 @@ export const annotationTypeHandlers: Record<
       callback(annotation.center, false);
       callback(annotation.radii, true);
     },
+    defaultProperties(
+      annotation: Ellipsoid,
+      layerPosition: Float32Array<ArrayBufferLike>[],
+      scales: Float64Array,
+      units: string[],
+    ) {
+      annotation;
+      layerPosition;
+      scales;
+      units;
+      return { properties: [], values: [] };
+    },
   },
 };
 
diff --git a/src/ui/annotations.ts b/src/ui/annotations.ts
index 051b9a4e1..49b1e63e9 100644
--- a/src/ui/annotations.ts
+++ b/src/ui/annotations.ts
@@ -1783,6 +1783,8 @@ export function UserLayerWithAnnotationsMixin<
                 icon.textContent = handler.icon;
                 positionGrid.appendChild(icon);
 
+                const annotationLayerPositions: Float32Array<ArrayBufferLike>[] =
+                  [];
                 if (layerRank !== 0) {
                   const { layerDimensionNames } = (
                     chunkTransform as ChunkTransformParameters
@@ -1800,6 +1802,7 @@ export function UserLayerWithAnnotationsMixin<
                     annotation,
                     chunkTransform as ChunkTransformParameters,
                     (layerPosition, isVector) => {
+                      annotationLayerPositions.push(layerPosition);
                       const copyButton = makeCopyButton({
                         title: "Copy position",
                         onClick: () => {
@@ -1854,6 +1857,24 @@ export function UserLayerWithAnnotationsMixin<
 
                 const { relationships, properties } = annotationLayer.source;
                 const sourceReadonly = annotationLayer.source.readonly;
+                const globalCoordinateSpace =
+                  this.manager.root.coordinateSpace.value;
+                const defaultProperties = annotationTypeHandlers[
+                  annotation.type
+                ].defaultProperties(
+                  annotation,
+                  annotationLayerPositions,
+                  globalCoordinateSpace.scales,
+                  globalCoordinateSpace.units,
+                );
+                const allProperties = [
+                  ...defaultProperties.properties,
+                  ...properties,
+                ];
+                const allValues = [
+                  ...defaultProperties.values,
+                  ...annotation.properties,
+                ];
 
                 // Add the ID to the annotation details.
                 const label = document.createElement("label");
@@ -1872,8 +1893,10 @@ export function UserLayerWithAnnotationsMixin<
                 label.appendChild(valueElement);
                 parent.appendChild(label);
 
-                for (let i = 0, count = properties.length; i < count; ++i) {
-                  const property = properties[i];
+                for (let i = 0, count = allProperties.length; i < count; ++i) {
+                  const property = allProperties[i];
+                  const value = allValues[i];
+
                   const label = document.createElement("label");
                   label.classList.add("neuroglancer-annotation-property");
                   const idElement = document.createElement("span");
@@ -1886,7 +1909,6 @@ export function UserLayerWithAnnotationsMixin<
                   if (description !== undefined) {
                     label.title = description;
                   }
-                  const value = annotation.properties[i];
                   const valueElement = document.createElement("span");
                   valueElement.classList.add(
                     "neuroglancer-annotation-property-value",