diff --git a/containers/libreportal/frontend/css/admin.css b/containers/libreportal/frontend/css/admin.css
index 11f5a92..bf2fffb 100644
--- a/containers/libreportal/frontend/css/admin.css
+++ b/containers/libreportal/frontend/css/admin.css
@@ -1132,6 +1132,50 @@ table.sys-apps tr:hover td { background: rgba(var(--text-rgb), 0.03); }
     color: rgba(var(--text-rgb), 0.5);
     font-size: 0.85rem;
 }
+/* Expandable per-app folder breakdown. */
+.sys-storage-app-row.is-clickable { cursor: pointer; }
+.sys-storage-caret,
+.sys-storage-caret-spacer {
+    display: inline-block;
+    width: 1em;
+    margin-right: 6px;
+    color: rgba(var(--text-rgb), 0.45);
+    transition: transform .15s ease;
+}
+.sys-storage-caret.is-open { transform: rotate(90deg); }
+.sys-storage-app-detail.is-collapsed { display: none; }
+.sys-storage-app-detail > td {
+    padding: 2px 12px 10px 30px;
+    background: rgba(var(--text-rgb), 0.02);
+}
+.sys-storage-folders { list-style: none; margin: 0; padding: 0; }
+.sys-storage-folders li {
+    display: flex;
+    align-items: center;
+    gap: 10px;
+    padding: 4px 0;
+    font-size: 0.82rem;
+    color: rgba(var(--text-rgb), 0.72);
+}
+.sys-storage-folder-path {
+    font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
+}
+.sys-storage-folder-size {
+    margin-left: auto;
+    font-variant-numeric: tabular-nums;
+    color: rgba(var(--text-rgb), 0.92);
+}
+.sys-storage-ext-badge {
+    flex-shrink: 0;
+    padding: 1px 6px;
+    border-radius: 4px;
+    font-size: 0.68rem;
+    background: rgba(var(--status-warning-rgb), 0.18);
+    color: var(--status-warning);
+}
 .sys-storage-card-meta {
     margin-top: 8px;
     display: flex;
diff --git a/containers/libreportal/frontend/js/components/admin/system-storage-page.js b/containers/libreportal/frontend/js/components/admin/system-storage-page.js
index 6e545aa..e53aa3f 100644
--- a/containers/libreportal/frontend/js/components/admin/system-storage-page.js
+++ b/containers/libreportal/frontend/js/components/admin/system-storage-page.js
@@ -19,6 +19,7 @@ class SystemStoragePage {
         this.rootId = rootId;
         this.data = null;
         this._timer = null;
+        this._expanded = new Set();   // app names whose folder breakdown is open
         this._onClick = this._onClick.bind(this);
     }
 
@@ -53,7 +54,19 @@ class SystemStoragePage {
             return;
         }
         const recl = e.target.closest('[data-storage-reclaim]');
-        if (recl) { this._reclaim(recl); }
+        if (recl) { this._reclaim(recl); return; }
+        // Expand/collapse an app's per-folder breakdown. Toggle the DOM directly
+        // (no re-render) and remember the state so the 30s refresh re-applies it.
+        const tog = e.target.closest('[data-app-toggle]');
+        if (tog) {
+            const app = tog.getAttribute('data-app-toggle');
+            if (this._expanded.has(app)) this._expanded.delete(app);
+            else this._expanded.add(app);
+            const open = this._expanded.has(app);
+            const detail = this.root()?.querySelector(`[data-app-detail="${CSS.escape(app)}"]`);
+            if (detail) detail.classList.toggle('is-collapsed', !open);
+            tog.querySelector('.sys-storage-caret')?.classList.toggle('is-open', open);
+        }
     }
 
     // Confirm, then run the safe reclaim task and re-read usage as it lands.
@@ -270,6 +283,7 @@ class SystemStoragePage {
         const appRows = (as && Array.isArray(as.apps)) ? as.apps : [];
         const appMax = appRows.reduce((m, a) => Math.max(m, a.bytes || 0), 0);
         const hasExternal = appRows.some(a => a.external_bytes > 0);
+        const cols = hasExternal ? 4 : 3;
         const appBody = appRows.length
             ? `<div class="sys-apps-wrap">
                 <table class="sys-apps">
@@ -277,12 +291,25 @@ class SystemStoragePage {
                     <tbody>
                         ${appRows.map(a => {
                             const pct = appMax ? ((a.bytes || 0) / appMax) * 100 : 0;
-                            return `<tr>
-                                <td class="sys-app-name">${fmt.escape(a.app)}</td>
+                            const mounts = Array.isArray(a.mounts) ? a.mounts : [];
+                            const open = this._expanded.has(a.app);
+                            // Each app row expands into its folders (the bind mounts
+                            // it stores data in), labelled by the in-container path.
+                            const folders = mounts.map(m => `
+                                <li>
+                                    <span class="sys-storage-folder-path" title="${fmt.escape(m.source || '')}">${fmt.escape(m.path || m.source || '—')}</span>
+                                    ${m.external ? '<span class="sys-storage-ext-badge">external</span>' : ''}
+                                    <span class="sys-storage-folder-size">${fmt.bytes(m.bytes || 0)}</span>
+                                </li>`).join('');
+                            return `<tr class="sys-storage-app-row${mounts.length ? ' is-clickable' : ''}"${mounts.length ? ` data-app-toggle="${fmt.escape(a.app)}"` : ''}>
+                                <td class="sys-app-name">${mounts.length ? `<span class="sys-storage-caret${open ? ' is-open' : ''}">▸</span>` : '<span class="sys-storage-caret-spacer"></span>'}${fmt.escape(a.app)}</td>
                                 <td>${fmt.bytes(a.bytes || 0)}</td>
                                 <td class="sys-storage-app-barcol"><span class="sys-storage-app-bar"><span style="width:${pct.toFixed(1)}%"></span></span></td>
                                 ${hasExternal ? `<td>${a.external_bytes ? fmt.bytes(a.external_bytes) : '—'}</td>` : ''}
-                            </tr>`;
+                            </tr>${mounts.length ? `
+                            <tr class="sys-storage-app-detail${open ? '' : ' is-collapsed'}" data-app-detail="${fmt.escape(a.app)}">
+                                <td colspan="${cols}"><ul class="sys-storage-folders">${folders}</ul></td>
+                            </tr>` : ''}`;
                         }).join('')}
                     </tbody>
                 </table>
diff --git a/scripts/webui/data/generators/system/webui_system_metrics.sh b/scripts/webui/data/generators/system/webui_system_metrics.sh
index 344958d..8d003fb 100644
--- a/scripts/webui/data/generators/system/webui_system_metrics.sh
+++ b/scripts/webui/data/generators/system/webui_system_metrics.sh
@@ -236,18 +236,21 @@ webuiSystemAppStorage() {
         return 0
     fi
 
-    # name|project|source for every bind mount. Compose project groups an app's
-    # containers; fall back to the container name when unlabelled (as webuiSystemApps).
+    # name|project|destination|source for every bind mount. Compose project
+    # groups an app's containers; fall back to the container name when unlabelled
+    # (as webuiSystemApps). The destination (container path, e.g. /var/lib/mysql)
+    # labels each folder in the per-app breakdown.
     local raw
     raw=$(runFileOp docker inspect $ids --format \
-'{{$n := .Name}}{{$p := index .Config.Labels "com.docker.compose.project"}}{{range .Mounts}}{{if eq .Type "bind"}}{{$n}}|{{$p}}|{{.Source}}
+'{{$n := .Name}}{{$p := index .Config.Labels "com.docker.compose.project"}}{{range .Mounts}}{{if eq .Type "bind"}}{{$n}}|{{$p}}|{{.Destination}}|{{.Source}}
 {{end}}{{end}}' 2>/dev/null)
 
-    declare -A app_local app_ext seen
-    local total_local=0 total_ext=0
+    # One JSON object per included mount; jq groups them into apps below.
+    declare -A seen
+    local mounts_stream=""
 
-    local cname proj src
-    while IFS='|' read -r cname proj src; do
+    local cname proj dest src
+    while IFS='|' read -r cname proj dest src; do
         [[ -z "$src" ]] && continue
         cname="${cname#/}"
         proj="${proj:-$cname}"
@@ -266,35 +269,30 @@ webuiSystemAppStorage() {
         local bytes
         bytes=$(runFileOp du -sxB1 -- "$src" 2>/dev/null | awk '{print $1+0; exit}')
         bytes="${bytes:-0}"
-        if [[ -n "$root_dev" && "$dev" == "$root_dev" ]]; then
-            app_local["$proj"]=$(( ${app_local["$proj"]:-0} + bytes ))
-            total_local=$(( total_local + bytes ))
-        else
-            app_ext["$proj"]=$(( ${app_ext["$proj"]:-0} + bytes ))
-            total_ext=$(( total_ext + bytes ))
-        fi
+        local ext="false"
+        [[ -n "$root_dev" && "$dev" == "$root_dev" ]] || ext="true"
+        mounts_stream+="$(jq -nc --arg app "$proj" --arg path "$dest" --arg source "$src" \
+            --argjson bytes "$bytes" --argjson external "$ext" \
+            '{app:$app, path:$path, source:$source, bytes:$bytes, external:$external}')"$'\n'
     done <<< "$raw"
 
+    # Group mounts → apps (each with its folder breakdown), largest first.
     local apps_json="[]"
-    local appnames
-    appnames=$(printf '%s\n' "${!app_local[@]}" "${!app_ext[@]}" 2>/dev/null | sort -u)
-    if [[ -n "$appnames" ]]; then
-        local stream="" p
-        while IFS= read -r p; do
-            [[ -z "$p" ]] && continue
-            local l="${app_local[$p]:-0}" e="${app_ext[$p]:-0}"
-            stream+="$(jq -nc --arg app "$p" --argjson l "$l" --argjson e "$e" \
-                '{app:$app, local_bytes:$l, external_bytes:$e, bytes:($l+$e)}')"$'\n'
-        done <<< "$appnames"
-        apps_json=$(printf '%s' "$stream" | jq -s 'sort_by(-.bytes)' 2>/dev/null)
+    if [[ -n "${mounts_stream//[$' \t\n']/}" ]]; then
+        apps_json=$(printf '%s' "$mounts_stream" | jq -s '
+            group_by(.app) | map({
+                app: .[0].app,
+                bytes: (map(.bytes) | add),
+                local_bytes: ([.[] | select(.external | not) | .bytes] | add // 0),
+                external_bytes: ([.[] | select(.external) | .bytes] | add // 0),
+                mounts: (sort_by(-.bytes) | map({path, source, bytes, external}))
+            }) | sort_by(-.bytes)' 2>/dev/null)
         [[ -z "$apps_json" ]] && apps_json="[]"
     fi
 
     local tmp; tmp=$(mktemp)
-    if jq -n --argjson apps "$apps_json" \
-        --argjson tl "$total_local" --argjson te "$total_ext" \
-        --arg now "$now_iso" \
-        '{apps:$apps, total_local:$tl, total_external:$te, total:($tl+$te), updated:$now}' \
+    if printf '%s' "$apps_json" | jq --arg now "$now_iso" \
+        '{apps: ., total: (map(.bytes) | add // 0), total_local: (map(.local_bytes) | add // 0), total_external: (map(.external_bytes) | add // 0), updated: $now}' \
         > "$tmp" 2>/dev/null; then
         runFileWrite "$final_file" < "$tmp"
     fi