Why and How to Regenerate Thumbnails in WordPress?

Themes give shape to your WordPress site and plugins enhance that shape with additional features. However, beauty always comes with certain cost. Themes and plugins that showcase lot of thumbnail images on the content area, sidebar and footer needs to register each image size in WordPress. When you change the theme or plugin, these image sizes also will change and you need to regenerate the images in your site to adapt to the new image sizes. In this article, we will explain when and how to regenerate thumbnails in WordPress.

When to Regenerate Thumbnails?

There are two situations, you may need to regenerate images in WordPress.

  • Whenever you change the theme, it is necessary to regenerate all your images. This process will generate new thumbnail images that can align on new theme and load aster.
  • Similarly, there are some plugins register custom image sizes. Examples include, WooCommerce, review plugins, related posts with images, etc. when you disable or change these types of plugins, it is necessary to regenerate your images.

Why Should You Regenerate Images?

There are many reasons for this:

  • Let’s say, the old theme uses featured image size as 1600×800 pixels and the new theme uses 900×500 pixels. Now that loading larger image for the smaller placeholder will impact the appearance of your theme. The images will not properly fit on the container and overlap on other content.
  • For the same above reason, loading different size of image will considerably impact your page loading time. Since speed is one of the ranking factors in Google Search, you should resize the image and properly load as per the theme’s requirement. Failing which will show you warnings in Google PageSpeed Insights tool like properly resize images.
  • Finally, unused thumbnail images of deleted themes and plugins will occupy storage space in your server. You can cleanup those images as part of your housekeeping to release storage space on your server.

How to Regenerate Thumbnails in WordPress?

WordPress has plugins for everything including for regenerating your images.

  • After changing your theme or plugin, login to your WordPress administrator dashboard.
  • Navigate to “Plugins > Add New” section and search for “regenerate thumbnails” in the search box.
  • Find Regenerate Thumbnails plugin, install and activate it on your site.
Install Regenerate Thumbnails Plugin
Install Regenerate Thumbnails Plugin

Choosing Correct Options for Regeneration

The plugin will add a menu item under “Settings” and go to “Settings > Regenerate Thumbnails” menu. You will see the following options to regenerate your images.

Regenerate Thumbnails in WordPress
Regenerate Thumbnails in WordPress
  • Skip regenerating existing correctly sized thumbnails – select this option to save time by skipping properly sized existing images.
  • Delete thumbnails for old unregistered sizes…. – select this option to delete all unused thumbnail images in your site. however, you need to thoroughly check the site for broken image links as some of the old thumbnails might be still linked somewhere on the site.
  • Regenerate thumbnails for all attachments – this is the option to regenerate all your images including the images on the post and page content.
  • Regenerate thumbnails for featured images – this is the optimal situation when changing themes as the plugin will only regenerate featured images and exclude all other normal images used on the posts/pages.

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Handling Regeneration Process

Select the options and click on the required button to start the regeneration process. You can view the progress of the regeneration and the plugin will show each image name after finishing the process in the log. Do not click on the image link which will take you to the edit screen and terminate the regeneration process. If you want to stop the progress, click on “Pause” button and restart again when you ready.

Regeneration in Progress
Regeneration in Progress

The process will take long time depending upon the number of images. You can also view the percentage of completion in the browser’s title bar to understand how much you may need to wait. After successful completion, you will see a message “All Done” with the time taken for the process.

Regeneration Done Successfully
Regeneration Done Successfully

Regenerating Images in Bulk and Individual

When you are in the plugin’s regeneration page, you can view all registered thumbnail image sizes by your theme and plugins as a list. This will give you an idea of how many images you need to regenerate so that you can be sure of the available server resources. For example, if you have 100 featured images and your site needs 10 image sizes then totally you need 1000 regenerated thumbnails. Due to this reason, the regeneration process is resource intensive and can bring down your site if you are doing on shared hosting environments like Bluehost or SiteGround. Therefore, do not run the regeneration for all images at once. The plugin offers solution to handle this situation – regenerate single or bulk images.

  • Go to “Media > Library” section to view all the uploaded images in your site.
  • Hover over any single image and click on the “Regenerate Thumbnails” option.
  • This will complete the process for the selected image.
Regenerate Single Image
Regenerate Single Image
  • For regenerating bulk images, select the images and click on the “Bulk actions” dropdown.
  • Select “Regenerate Thumbnails” option from the list and click “Apply” button.
  • In this way, you can regenerate bulk images like 20 to avoid server crashing. You can click on the “Screen Option” button showing on the top right corner and select the number of items to be displayed on a single page.
Bulk Regenerate Thumbnails
Bulk Regenerate Thumbnails

Tips to Reduce Thumbnails Images

As mentioned, you can delete the unused thumbnail images to save storage space. However, there is another trick to reduce the number of thumbnails generated on your site. WordPress by default generates small, medium and large thumbnails for each image you upload. Most commercial themes do not use these image sizes as they use their own custom sizes. You can check the list of thumbnails as explained above and disable all default WordPress thumbnails by going to “Settings > Media” section. Simply make all the sizes for height and width to zero and save your changes to disable default thumbnail generation.

Default Thumbnails Sizes
Default Thumbnails Sizes

Also avoid using magazine style themes and gallery plugins that generate plenty of thumbnail images.

Note: On the regeneration page, the plugin will suggest an alternative to use Photon feature from Jetpack plugin. This is called “Site Accelerator” in the latest Jetpack plugin version. We strongly recommend NOT using this option due to limitations as given in the official Jetpack site.

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