What are Thumbnail Sizes?

In WordPress, thumbnail sizes are built-in sizing features that enable you to set preferred sizing for all images uploaded to the Media Library.

More About Thumbnail Sizes

You can define thumbnail sizes by navigating to Settings > Media and locating the Image sizes section. On this page, you can identify the maximum dimensions in pixels to use when adding any future images to the Media Library.

There are three default values in addition to a file’s original resolution:

  1. Thumbnail size: 150x150px
  2. Medium size: 300x300px (max)
  3. Large size: 1024x1024px (max)

WordPress will use these values for all future image uploads. However, your changes will not be retroactive. You will need to resize any previously-uploaded media or use a plugin to help you regenerate new sizes for any older images.

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