diff --git a/src/web_interface/file_tree/file_tree_node.py b/src/web_interface/file_tree/file_tree_node.py
index 50d7ac978..19f73b897 100644
--- a/src/web_interface/file_tree/file_tree_node.py
+++ b/src/web_interface/file_tree/file_tree_node.py
@@ -33,7 +33,7 @@ def __init__(  # noqa: PLR0913
         self.root_uid = root_uid
         self.virtual = virtual
         self.name = name
-        self.size = size
+        self._size = size
         self.mode = mode
         self.type = mime_type
         self.has_children = has_children
@@ -109,3 +109,9 @@ def get_id(self) -> tuple[str, bool]:
         :return: The id, consisting of the name and ``virtual`` (whether the node is a directory)
         """
         return self.name, self.virtual
+
+    @property
+    def size(self) -> int | None:
+        if self._size is None and self.virtual:  # virtual = directory
+            self._size = sum(child.size for child in self.get_list_of_child_nodes() if child.size is not None)
+        return self._size
diff --git a/src/web_interface/file_tree/jstree_conversion.py b/src/web_interface/file_tree/jstree_conversion.py
index c34d931de..a1645e98d 100644
--- a/src/web_interface/file_tree/jstree_conversion.py
+++ b/src/web_interface/file_tree/jstree_conversion.py
@@ -25,7 +25,8 @@ def convert_to_jstree_node(node: FileTreeNode):
 
 
 def _get_directory_jstree_node(node: FileTreeNode):
-    return _get_jstree_node_contents(f'{node.name}', '#', '/static/file_icons/folder.svg')
+    label = f'<b>{node.name}</b> (<span style="color:gray;">{human_readable_file_size(node.size)}</span>)'
+    return _get_jstree_node_contents(label, '#', '/static/file_icons/folder.svg')
 
 
 def _get_not_analyzed_jstree_node(node: FileTreeNode):