diff --git a/src/Plugin/EntityBrowser/Display/IFrame.php b/src/Plugin/EntityBrowser/Display/IFrame.php
index fe3e91c..4aef4fe 100644
--- a/src/Plugin/EntityBrowser/Display/IFrame.php
+++ b/src/Plugin/EntityBrowser/Display/IFrame.php
@@ -227,6 +227,7 @@ class IFrame extends DisplayBase implements DisplayRouterInterface {
       '#type' => 'textfield',
       '#title' => $this->t('Width of the iFrame'),
       '#default_value' => $configuration['width'],
+      '#description' => $this->t('Positive integer for absolute size or a relative size in percentages.'),
     ];
 
     $form['height'] = [