Regenerate Thumbnails is a useful WordPress plugin that you can use to regenerate the thumbnail sizes of image files. You can regenerate thumbnails of recently acquired image files as well as the ones you’ve had for a while When you’ve altered your WordPress theme, you should regenerate your thumbnails because the new images will be a different size so they can fit your new theme. 

Old images will remain the same until you regenerate them. You can complete this process for individual or multiple image uploads. WP-CLI or the Jetpack Photon Module are alternative plugins that perform similar functions. 

How to use the plugin

Find Regenerate Thumbnails on the Add Plugins page of your WordPress website. Then, you must install and activate the Regenerate Thumbnails plugin.

Navigate to Tools -> Regenerate Thumbnails and change the settings. You’ll see a list of all the thumbnail sizes registered on the screen, which you can then change to the same size. Click either ‘regenerate all thumbnails’ or ‘regenerate featured thumbnails only’. 

Why regenerate thumbnails?

Here are a few reasons to use this plugin to regenerate thumbnails:

• If you alter your WordPress theme, it will have different thumbnail settings. You regenerate thumbnails so that all of them on your site will match. 
• If you don’t change the theme but upgrade to the newest release of the same theme, your earlier image settings might not work and you might have to regenerate them.  
• If you want to change the size of your thumbnail in the same theme, you can do it in Media Settings. After that, you might want to regenerate the thumbnails for all your blog posts so that they conform.

How big should your thumbnails be?

The default maximum size of thumbnails in WordPress is 150x150 pixels, a square. The default medium size is 600x600 pixels, and the large size 1024x1024 pixels. These sizes maintain uniformity in your blog no matter what their actual dimensions are. 

Additionally, you can increase or decrease all your thumbnail sizes by going to Media Settings in your WordPress blog. There you can set your default size irrespective of the dimensions above. 

Useful features

Being able to regenerate large numbers of thumbnails simultaneously on your blog to make them uniform is a very useful feature in WordPress. Changing them manually would take a long time if you’ve used many images.