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How to Regenerate Thumbnails or Set New Image Sizes in WordPress

How to Regenerate Thumbnails or Set New Image Sizes in WordPress

Have you ever wanted to change or regenerate the current post thumbnails (i.e. featured images) or themes for worrying about the image sizes couldn’t fit appropriately? To tell the truth, if you make some changes on WordPress site’s themes, your new images look fine while the previously uploaded images sometimes will look distorted or show improperly. To go out from this embarrassing situation, it is advisable to regenerate thumbnails or set new images as follows.

Something You Need to Know Before Starting out

Regenerate Thumbnails & Add New Image SizesWordPress, as the most user-friendly content management system, generates three additional copies of the uploaded images in different dimensions in the Media Library section. The reason why WordPress has to do so is that our uploaded images sometimes are too large to show directly in web application. In this way, it shows the most proper image size so as to make images responsive as possible.

Pay attention that you can change the default value of the images sizes on the settings page, but the dimensions of the uploaded images won’t change at all. Thus, as is noted above, you need to regenerate thumbnails for the previous uploads by following our steps in below.

Adjust the Thumbnails for New Uploads

Before applying new thumbnails for the old files, you need to adjust the image size for new uploads firstly. To do so, you can follow the root of “Settings > Media.” As is showed in the following “Media Settings” window, there are three default image sizes, including “Thumbnail”, “Medium” and “Large”. You can notice that there is a special checkbox for cropping the “Thumbnail Size” to exact dimensions as you like.

As for the “Medium Size” and “Large Size” options, you can specify the maximum dimensions for image “Width” and “Height”. In this case, it is possible to resize large images accordingly and generate a new image that is available to insert into a post/page at full size. Having customized new dimensions for future media files, you should click “Save Changes” to make it work.

Regenerate Thumbnails & Add New Image Sizes

Apply Customized Thumbnail Image Size to the Uploaded Files

Having done those above steps, it’s time to regenerate new thumbnail dimensions for the old uploads. The best way to achieve this goal is to use the popular WordPress plugin – Regenerate Thumbnails. This plugin enables you to delete old images and in the meantime regenerate thumbnails for image attachments in bulk.

To install and activate the Regenerate Thumbnails plugin, you just need to search this plugin in the “Plugins > Add New” section and click the “Install” and “Activate” buttons to put it into effect. If everything goes successfully, you can find it in the “Installed Plugin” as follows.

Regenerate Thumbnails & Add New Image Sizes

Generally speaking, you are empowered to generate thumbnails in bulk and separately. To regenerate all thumbnails, you can go into the “Tools” section to choose the “Regen.Thumbnails” option. As is showed in the following screenshot, you can regenerate all images in the specified sizes by clicking the “Regenerate All Thumbnails” button. Note that this thumbnail generation is irreversible, but you are able to covert thumbnail dimensions into the old values by clicking this button again.

Regenerate Thumbnails & Add New Image Sizes

It takes a while to generate all thumbnails especially there are too many old uploads. You should be patient during the whole process. At the same time, you also can pause it by clicking “Abort Resizing Images” option at any time.

Regenerate Thumbnails & Add New Image Sizes

Alternatively, you are allowed to resize selected images manually by entering the “Media > Library” section. In the following window of Media Library, click the “Regenerate Thumbnails” option lying under the “Bulk Actions”. Next, choose the images to resize to thumbnail size by clicking in the correspondent checkbox.

Regenerate Thumbnails & Add New Image Sizes

Finally, don’t forget to click “Apply” button to start resizing thumbnails. In the following screenshot, there is a processing bar for you to check whether the thumbnails are successfully regenerated. Do not switch to other pages until the whole regeneration is 100% completed.

Regenerate Thumbnails & Add New Image Sizes

Notes: The regenerated image sizes won’t affect the older uploads, and it just creates additional copies of images in new specified dimensions. Of course, you can delete the previous image sizes that are unused all the time.


Susan Rose is a freelance writer who has a deep knowledge about WordPress. She loves everything related to website building since the freshman year at Christopher Newport University, and loves to share her experience with people all over all the world. In the daily life, Susan loves detective novels as it can train her logical thinking and creativity.