diff --git a/webui/html/app.js b/webui/html/app.js
index c556e15..4543999 100644
--- a/webui/html/app.js
+++ b/webui/html/app.js
@@ -837,6 +837,25 @@ function formatModified(isoString) {
   return `${date} ${time}`;
 }
 
+function formatFileSize(bytes) {
+  if (typeof bytes !== "number" || !Number.isFinite(bytes) || bytes < 0) {
+    return "-";
+  }
+  if (bytes < 1024) {
+    return `${bytes} B`;
+  }
+  if (bytes < 1024 ** 2) {
+    return `${Math.round(bytes / 1024)} KB`;
+  }
+  if (bytes < 1024 ** 3) {
+    return `${(bytes / (1024 ** 2)).toFixed(1)} MB`;
+  }
+  if (bytes < 1024 ** 4) {
+    return `${(bytes / (1024 ** 3)).toFixed(1)} GB`;
+  }
+  return `${(bytes / (1024 ** 4)).toFixed(1)} TB`;
+}
+
 function createBrowseItem(pane, entry, kind) {
   const li = document.createElement("li");
   li.className = "selectable";
@@ -888,7 +907,7 @@ function createBrowseItem(pane, entry, kind) {
 
   const size = document.createElement("span");
   size.className = "entry-size";
-  size.textContent = kind === "directory" ? "-" : String(entry.size);
+  size.textContent = kind === "directory" ? "-" : formatFileSize(entry.size);
   li.append(size);
 
   const modified = document.createElement("span");