diff --git a/data/units.json b/data/units.json
index 738768a..35f1340 100644
--- a/data/units.json
+++ b/data/units.json
@@ -24,7 +24,9 @@
       "labelPlural": "barrels",
       "symbol": "bbl",
       "group": "dickloads",
-      "toBase": 19
+      "toBase": 13.319,
+      "description": "Weight is based on pure water at 4 degrees celsius.",
+      "hidden": false
     },
     {
       "id": "hogshead",
@@ -101,6 +103,14 @@
       "group": "another-group",
       "toBase": 1,
       "hidden": true
+    },
+    {
+      "id": "us-fluid-bbl",
+      "label": "US fluid barrel",
+      "labelPlural": "US fluid barrels",
+      "symbol": "us fluid bbl",
+      "group": "dickloads",
+      "toBase": 9.9894438
     }
   ],
   "groups": [
diff --git a/src/routes/admin/+page.svelte b/src/routes/admin/+page.svelte
index 067a90c..0cf17a9 100644
--- a/src/routes/admin/+page.svelte
+++ b/src/routes/admin/+page.svelte
@@ -918,8 +918,8 @@
       <div onkeydown={onUnitFormKeydown}>
       <h3>{unitFormNew ? 'New Unit' : 'Edit Unit'}</h3>
       <label>
-        ID {#if !unitFormNew}<small class="muted">(readonly)</small>{/if}
-        <input type="text" bind:value={unitForm.id} readonly={!unitFormNew} placeholder="e.g. my-unit"
+        ID {#if !unitFormNew}<small class="muted">(changing will update all references)</small>{/if}
+        <input type="text" bind:value={unitForm.id} placeholder="e.g. my-unit"
           class:field-error={unitFieldError === 'unit-id'}
           oninput={() => unitFormNew && onUnitIdInput()} />
       </label>
@@ -977,8 +977,8 @@
       <div onkeydown={onGroupFormKeydown}>
       <h3>{groupFormNew ? 'New Group' : 'Edit Group'}</h3>
       <label>
-        ID {#if !groupFormNew}<small class="muted">(readonly)</small>{/if}
-        <input type="text" bind:value={groupForm.id} readonly={!groupFormNew} placeholder="e.g. my-group"
+        ID {#if !groupFormNew}<small class="muted">(changing will update all references)</small>{/if}
+        <input type="text" bind:value={groupForm.id} placeholder="e.g. my-group"
           class:field-error={groupFieldError === 'group-id'}
           oninput={() => groupFormNew && onGroupIdInput()} />
       </label>
diff --git a/src/routes/admin/api/groups/[id]/+server.ts b/src/routes/admin/api/groups/[id]/+server.ts
index 0be428a..091015b 100644
--- a/src/routes/admin/api/groups/[id]/+server.ts
+++ b/src/routes/admin/api/groups/[id]/+server.ts
@@ -1,9 +1,18 @@
 import { json } from '@sveltejs/kit';
 import { loadData, saveData } from '$lib/server/data';
-import { authRequest } from '$lib/server/auth';
+import { authRequest, KEBAB_RE } from '$lib/server/auth';
 import type { RequestHandler } from './$types';
 import type { Group } from '$lib/types';
 
+function renameIdInDescription(desc: string, oldId: string, newId: string): string {
+  const re = new RegExp(`\\{${escapeRegex(oldId)}(:[^}]*)?\\}`, 'g');
+  return desc.replace(re, (_, suffix) => `{${newId}${suffix ?? ''}}`);
+}
+
+function escapeRegex(s: string): string {
+  return s.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
+}
+
 export const PUT: RequestHandler = async ({ request, params }) => {
   if (!authRequest(request)) return json({ error: 'Unauthorized' }, { status: 401 });
 
@@ -17,6 +26,18 @@ export const PUT: RequestHandler = async ({ request, params }) => {
 
   const patch = body as Partial<Group>;
   const currentGroup = data.groups[gIdx];
+  const newId = patch.id;
+  const idChanging = newId !== undefined && newId !== id;
+
+  // Validate new ID if changing
+  if (idChanging) {
+    if (!KEBAB_RE.test(newId!)) {
+      return json({ error: 'id must be kebab-case' }, { status: 400 });
+    }
+    if (data.groups.some((g) => g.id === newId)) {
+      return json({ error: `Group id '${newId}' already exists` }, { status: 400 });
+    }
+  }
 
   // Special case: changing baseUnitId requires recalculating all unit toBase values
   if (patch.baseUnitId !== undefined && patch.baseUnitId !== currentGroup.baseUnitId) {
@@ -25,10 +46,7 @@ export const PUT: RequestHandler = async ({ request, params }) => {
     if (!newBaseUnit) {
       return json({ error: `baseUnitId '${newBaseId}' not found in this group` }, { status: 400 });
     }
-
-    const X = newBaseUnit.toBase; // Current toBase of the new base unit
-    // Recalculate all units in this group: unit.toBase = unit.toBase / X
-    // Then set new base unit toBase = 1.0
+    const X = newBaseUnit.toBase;
     for (const unit of data.units) {
       if (unit.group === id) {
         unit.toBase = unit.id === newBaseId ? 1.0 : unit.toBase / X;
@@ -38,8 +56,22 @@ export const PUT: RequestHandler = async ({ request, params }) => {
 
   const updated: Group = { ...currentGroup, ...patch };
   data.groups[gIdx] = updated;
-  saveData(data);
 
+  // Cascade ID rename across the dataset
+  if (idChanging) {
+    // Update unit.group references
+    for (const u of data.units) {
+      if (u.group === id) u.group = newId!;
+    }
+    // Update {id:*} placeholders in all unit descriptions
+    for (const u of data.units) {
+      if (u.description) {
+        u.description = renameIdInDescription(u.description, id, newId!);
+      }
+    }
+  }
+
+  saveData(data);
   return json(updated);
 };
 
diff --git a/src/routes/admin/api/units/[id]/+server.ts b/src/routes/admin/api/units/[id]/+server.ts
index 5719948..0c36869 100644
--- a/src/routes/admin/api/units/[id]/+server.ts
+++ b/src/routes/admin/api/units/[id]/+server.ts
@@ -4,6 +4,17 @@ import { authRequest, KEBAB_RE } from '$lib/server/auth';
 import type { RequestHandler } from './$types';
 import type { Unit } from '$lib/types';
 
+/** Replace all {oldId}, {oldId:field} placeholder tokens in a description string. */
+function renameIdInDescription(desc: string, oldId: string, newId: string): string {
+  // Match {oldId} and {oldId:anything}
+  const re = new RegExp(`\\{${escapeRegex(oldId)}(:[^}]*)?\\}`, 'g');
+  return desc.replace(re, (_, suffix) => `{${newId}${suffix ?? ''}}`);
+}
+
+function escapeRegex(s: string): string {
+  return s.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
+}
+
 export const PUT: RequestHandler = async ({ request, params }) => {
   if (!authRequest(request)) return json({ error: 'Unauthorized' }, { status: 401 });
 
@@ -16,14 +27,16 @@ export const PUT: RequestHandler = async ({ request, params }) => {
   if (idx === -1) return json({ error: 'Unit not found' }, { status: 404 });
 
   const patch = body as Partial<Unit>;
+  const newId = patch.id;
+  const idChanging = newId !== undefined && newId !== id;
 
-  // If id is changing, validate new id
-  if (patch.id !== undefined && patch.id !== id) {
-    if (!KEBAB_RE.test(patch.id)) {
+  // Validate new ID if changing
+  if (idChanging) {
+    if (!KEBAB_RE.test(newId!)) {
       return json({ error: 'id must be kebab-case' }, { status: 400 });
     }
-    if (data.units.some((u) => u.id === patch.id)) {
-      return json({ error: `Unit id '${patch.id}' already exists` }, { status: 400 });
+    if (data.units.some((u) => u.id === newId)) {
+      return json({ error: `Unit id '${newId}' already exists` }, { status: 400 });
     }
   }
   if (patch.toBase !== undefined && patch.toBase <= 0) {
@@ -35,8 +48,22 @@ export const PUT: RequestHandler = async ({ request, params }) => {
 
   const updated: Unit = { ...data.units[idx], ...patch };
   data.units[idx] = updated;
-  saveData(data);
 
+  // Cascade ID rename across the dataset
+  if (idChanging) {
+    // Update group.baseUnitId references
+    for (const g of data.groups) {
+      if (g.baseUnitId === id) g.baseUnitId = newId!;
+    }
+    // Update {id:*} placeholders in all unit descriptions
+    for (const u of data.units) {
+      if (u.description) {
+        u.description = renameIdInDescription(u.description, id, newId!);
+      }
+    }
+  }
+
+  saveData(data);
   return json(updated);
 };