diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2d86a69..a74019d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,13 @@ and this project uses [Semantic Versioning](https://semver.org/spec/v2.0.0.html)
 
 ## [Unreleased]
 
+### Fixed
+
+- **Cache sizes say they are bytes.** The Drivers tab, the engine counters, a driver's status and the
+  Architecture view's tooltip showed a driver's cache as a bare number, such as `465`. That reads as 465
+  queued events, but the engine reports the size in bytes; 465 bytes was two events. They now read
+  `465 bytes`. **view** beside the size still lists and counts the events.
+
 ## [0.85.0] - 2026-11-02
 
 Needs DirXMLDev 0.62.0.
diff --git a/web/src/components/ArchitectureView.tsx b/web/src/components/ArchitectureView.tsx
index 71f8ece..b977ebc 100644
--- a/web/src/components/ArchitectureView.tsx
+++ b/web/src/components/ArchitectureView.tsx
@@ -1,6 +1,7 @@
 import { useEffect, useMemo, useRef, useState } from "react";
 import { api } from "../api";
 import { EnvPicker, useEnvironment } from "../env";
+import { cacheBytes } from "../drivers";
 import type { ArchApplication, Architecture, DriverState, Selection } from "../types";
 
 /**
@@ -275,7 +276,7 @@ export function ArchitectureView({ revision, onSelect }: { revision: string; onS
     const midX = (fromX + toX) / 2;
     const vaultY = Math.min(Math.max(cy, st0.y + 24), st0.y + st0.h - 24);
     const st = states?.[a.driver];
-    const tip = `${a.driver}${a.vaultOnly ? " (serves the vault, no external system)" : ""}\n${a.shimClass ?? "no shim class"}\n${a.counts.policies} policies · ${a.counts.entitlements} entitlements · ${a.counts.resources} resources${a.counts.forms + a.counts.prds > 0 ? ` · ${a.counts.forms} forms · ${a.counts.prds} PRDs` : ""}${st ? `\n${st.state}${st.cacheSize ? ` · cache ${st.cacheSize}` : ""}` : ""}`;
+    const tip = `${a.driver}${a.vaultOnly ? " (serves the vault, no external system)" : ""}\n${a.shimClass ?? "no shim class"}\n${a.counts.policies} policies · ${a.counts.entitlements} entitlements · ${a.counts.resources} resources${a.counts.forms + a.counts.prds > 0 ? ` · ${a.counts.forms} forms · ${a.counts.prds} PRDs` : ""}${st ? `\n${st.state}${st.cacheSize ? ` · cache ${cacheBytes(st.cacheSize)}` : ""}` : ""}`;
     return (
       <g key={a.driver}>
         <path className="arch-conn" d={`M${fromX},${cy} C${midX},${cy} ${midX},${vaultY} ${toX},${vaultY}`} />
diff --git a/web/src/components/VaultView.tsx b/web/src/components/VaultView.tsx
index c02412d..57f405b 100644
--- a/web/src/components/VaultView.tsx
+++ b/web/src/components/VaultView.tsx
@@ -4,6 +4,7 @@ import { Fragment, useEffect, useRef, useState } from "react";
 import { ApiError, GIT_CHANGED, api } from "../api";
 import { EnvPicker, useEnvironment } from "../env";
 import { CachePanel } from "./CachePanel";
+import { cacheBytes } from "../drivers";
 import { EventsView } from "./EventsView";
 import { TraceViewer } from "./TraceViewer";
 import { CaptureSteps, ProductionCheck } from "./ProductionCheck";
@@ -1134,7 +1135,7 @@ function Drivers({ env, onFix, onSelect, onSaved }: { env: string; onFix: () =>
                   </button>
                 </td>
                 <td className="nowrap">
-                  {d.cacheSize ?? ""}{" "}
+                  {cacheBytes(d.cacheSize)}{" "}
                   <button className="mini" onClick={() => setCacheOf(cacheOf === d.name ? null : d.name)} title="The queued events: view them, save them as a simulator case, clear the cache" data-testid={"cache-view-" + d.name}>
                     {cacheOf === d.name ? "hide" : "view"}
                   </button>
@@ -1228,8 +1229,8 @@ function EngineStrip({ env }: { env: string }) {
             {data.stats.drivers.map((d) => (
               <tr key={d.name}>
                 <td>{d.name}</td>
-                <td>{d.cacheSize}</td>
-                <td>{d.unprocessedSize}</td>
+                <td>{cacheBytes(d.cacheSize)}</td>
+                <td>{cacheBytes(d.unprocessedSize)}</td>
                 <td>{d.reportedEvents}</td>
                 <td>{d.commands}</td>
               </tr>
@@ -1326,7 +1327,7 @@ function DriverManagePanel({ env, driver, armed, confirm, onSelect, onClose }: {
             <tbody>
               <tr><td>DN</td><td className="small"><code>{status.dn}</code></td></tr>
               <tr><td>State</td><td>{status.state} · start option {status.startOption}</td></tr>
-              <tr><td>Cache</td><td>{status.cacheSize} · unprocessed {status.unprocessedSize}</td></tr>
+              <tr><td>Cache</td><td>{cacheBytes(status.cacheSize)} · unprocessed {cacheBytes(status.unprocessedSize)}</td></tr>
               <tr><td>Trace</td><td>level {status.traceLevel ?? "-"} · file {status.traceFile || "-"}</td></tr>
               <tr><td>Named passwords</td><td className="small">{(status.namedPasswords ?? []).length === 0 ? <span className="muted">none</span> : (status.namedPasswords ?? []).join(", ")}</td></tr>
             </tbody>
diff --git a/web/src/drivers.test.ts b/web/src/drivers.test.ts
new file mode 100644
index 0000000..c85c3e0
--- /dev/null
+++ b/web/src/drivers.test.ts
@@ -0,0 +1,14 @@
+import { describe, expect, it } from "vitest";
+import { cacheBytes } from "./drivers";
+
+describe("cacheBytes", () => {
+  it("gives the engine's cache size its unit", () => {
+    expect(cacheBytes("465")).toBe("465 bytes");
+    expect(cacheBytes(0)).toBe("0 bytes");
+  });
+  it("leaves what isn't a size alone", () => {
+    expect(cacheBytes("?")).toBe("?");
+    expect(cacheBytes(undefined)).toBe("");
+    expect(cacheBytes("")).toBe("");
+  });
+});
diff --git a/web/src/drivers.ts b/web/src/drivers.ts
index b21ddb7..a2f3561 100644
--- a/web/src/drivers.ts
+++ b/web/src/drivers.ts
@@ -11,3 +11,12 @@ export function isUserApplication(d: { shimClass?: string | null; forms?: unknow
 export function userApplicationDrivers(drivers: DriverOutline[]): DriverOutline[] {
   return drivers.filter(isUserApplication);
 }
+
+/**
+ * A driver's cache size as the engine reports it, with its unit: bytes, not a count of events (viewing the
+ * cache counts them). 465 bytes was two events on a test vault. Anything that isn't a number shows as it is.
+ */
+export function cacheBytes(size: string | number | null | undefined): string {
+  if (size === null || size === undefined || size === "") return "";
+  return /^\d+$/.test(String(size)) ? `${size} bytes` : String(size);
+}