diff --git a/core/modules/file/file.module b/core/modules/file/file.module
index 8eef9c40dc10..53483c16f9fb 100644
--- a/core/modules/file/file.module
+++ b/core/modules/file/file.module
@@ -1502,6 +1502,7 @@ function template_preprocess_file_link(&$variables) {
   // Set file classes to the options array.
   $variables['attributes'] = new Attribute($variables['attributes']);
   $variables['attributes']->addClass($classes);
+  $variables['file_size'] = format_size($file->getSize());
 
   $variables['link'] = \Drupal::l($link_text, Url::fromUri($url, $options));
 }
diff --git a/core/modules/file/templates/file-link.html.twig b/core/modules/file/templates/file-link.html.twig
index 44cbd7f6892e..9fb2fa67c560 100644
--- a/core/modules/file/templates/file-link.html.twig
+++ b/core/modules/file/templates/file-link.html.twig
@@ -6,6 +6,7 @@
  * Available variables:
  * - attributes: The HTML attributes for the containing element.
  * - link: A link to the file.
+ * - file_size: The size of the file.
  *
  * @see template_preprocess_file_link()
  *
@@ -13,3 +14,7 @@
  */
 #}
 <span{{ attributes }}>{{ link }}</span>
+{% if file_size %}
+  {# @todo remove class before Drupal 9.0.0 #}
+  <span class="file-size">({{ file_size }})</span>
+{% endif %}
diff --git a/core/modules/image/image.field.inc b/core/modules/image/image.field.inc
index bf69b90442ec..1afdde2fdda8 100644
--- a/core/modules/image/image.field.inc
+++ b/core/modules/image/image.field.inc
@@ -21,11 +21,6 @@ function template_preprocess_image_widget(&$variables) {
 
   $variables['attributes'] = ['class' => ['image-widget', 'js-form-managed-file', 'form-managed-file', 'clearfix']];
 
-  if (!empty($element['fids']['#value'])) {
-    $file = reset($element['#files']);
-    $element['file_' . $file->id()]['filename']['#suffix'] = ' <span class="file-size">(' . format_size($file->getSize()) . ')</span> ';
-  }
-
   $variables['data'] = [];
   foreach (Element::children($element) as $child) {
     $variables['data'][$child] = $element[$child];
diff --git a/core/themes/classy/templates/field/file-link.html.twig b/core/themes/classy/templates/field/file-link.html.twig
index 11170c0c0f65..78384e653307 100644
--- a/core/themes/classy/templates/field/file-link.html.twig
+++ b/core/themes/classy/templates/field/file-link.html.twig
@@ -7,8 +7,10 @@
  * - attributes: The HTML attributes for the containing element.
  * - link: A link to the file.
  * - icon: The icon image representing the file type.
+ * - file_size: The size of the file.
  *
  * @see template_preprocess_file_link()
+ * @see stable_preprocess_image_widget()
  */
 #}
 {{ attach_library('classy/file') }}
diff --git a/core/themes/stable/stable.theme b/core/themes/stable/stable.theme
index 456a4ad39fab..5812f890a185 100644
--- a/core/themes/stable/stable.theme
+++ b/core/themes/stable/stable.theme
@@ -23,3 +23,13 @@ function stable_preprocess_links(&$variables) {
     }
   }
 }
+
+/**
+ * Implements hook_preprocess_image_widget().
+ */
+function stable_preprocess_image_widget(&$variables) {
+  if (!empty($variables['element']['fids']['#value'])) {
+    $file = reset($variables['element']['#files']);
+    $variables['data']['file_' . $file->id()]['filename']['#suffix'] = ' <span class="file-size">(' . format_size($file->getSize()) . ')</span> ';
+  }
+}
diff --git a/core/themes/stable/templates/field/file-link.html.twig b/core/themes/stable/templates/field/file-link.html.twig
index 0424830f574b..7da6aa466105 100644
--- a/core/themes/stable/templates/field/file-link.html.twig
+++ b/core/themes/stable/templates/field/file-link.html.twig
@@ -6,8 +6,10 @@
  * Available variables:
  * - attributes: The HTML attributes for the containing element.
  * - link: A link to the file.
+ * - file_size: The size of the file.
  *
  * @see template_preprocess_file_link()
+ * @see stable_preprocess_image_widget()
  */
 #}
 <span{{ attributes }}>{{ link }}</span>