How to set the best WordPress image size for quick loading

The content management system WordPress offers the possibility to use individual image formats in addition to standard image sizes. We present important steps to customized image sizes, based on WordPress 6.0.3.

The default image sizes in WordPress

The file size of images embedded on a website has a great impact on its loading speed. Optimal image formats shorten the loading time and reduce the memory load on the server. The WordPress CMS offers a set of standardized image sizes on the server when uploading media.

WordPress standard image sizes Size (L x H) in pixels Aspect ratio
Preview images 150 x 150 Can be deactivated
Medium 300 x 300 Retained
Large 1024 x 1024 Retained
Original image As uploaded Retained
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Save WordPress images in the backend and adjust sizes

These image sizes are defined in the WordPress settings and can be adjusted there within certain limits. To do this, go to “Settings” > “Media” in the backend.

Image size settings in the WordPress backend
You can customize the preset default image sizes in the WordPress dashboard.

After the media upload, there are additional files in the media library. The directory for this is https://mydomain.com/wp-content/uploads/ or https://mydomain.com/wp-content/uploads/2022/11/ (if month- and year-based folders are enabled). For example, an image is in the following files:

  • sample-image-1024x683.jpg
  • sample-image-150x150.jpg
  • sample-image-1536x1024.jpg
  • sample-image-2048x1365.jpg
  • sample-image-300x200.jpg
  • sample-image-620x413.jpg
  • sample-picture-scaled.jpg (2.560 x 1.707 px)
  • sampleimage.jpg (the original)

This provides the best image sizes for most WordPress pages or posts. Images for upload to the media library should not be larger than 1,920 pixels at the long edge of the image. They can be resized before uploading with free image editing programs to avoid unpleasant surprises. That applies to WebP image format, which is not natively supported by all browsers.

These are the recommended image sizes for use in WordPress themes:

WordPress image sizes Size (L x H) in pixels
Logos 200 x 100
Preview images 150 x 150
Background images 1920 x 1080
Post images in portrait format 900 x 1200
Post images in landscape format 1200 x 900
Header images (banner) 1048 x 250
Slider images (theme dependent) Up to 1920 x ca. 600
Common image sizes in WordPress
Commonly used image sizes for WordPress websites at a glance. Photo source: ESB Professional/shutterstock.com

The concrete required image dimensions depend on the components and structure of a WordPress theme. They can be found in the documentation of the respective theme.

Resize images in the WordPress media library

WordPress image sizes can also be adjusted. Besides changing the original image dimensions, cropping, rotating and flipping are possible. For example, to create a slider photo from an image with larger dimensions in the media library, proceed as follows:

Step 1: Select image in the media library and click “Edit image”

Image editing in WordPress library
Select an image from the WordPress media library for custom image resizing. Photo source: ESB Professional/shutterstock.com

Step 2: Set editing method and size

Set new image size in WordPress library
Change the image to the desired size using the crop editing method

It is worth noting that the crop button must be used twice: once to activate the function and then a second time after setting the image dimensions to perform the operation.

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Step 3: Save image to media library

Save resized image to WordPress library
“Save” will save the resized image to the WordPress library

After saving the scaled image, the upload folder contains the file

  • preview-image-scaled-e1667121439976.jpg

in another five formats with the automatically assigned ID …-e1667121439976. The newly created image sizes can be selected from the media library in the Gutenberg editor when inserting or exchanging them. The pixel dimensions of the image are then also available there.

Tip

If your chosen WordPress theme doesn’t offer sliders, you can take a look at the range of WordPress slider plugins.

Adjust image size when inserting into the WordPress content

The images from the WordPress media library are inserted into the content. This enables sizes to be adjusted afterwards within broad limits. The WordPress Gutenberg editor offers much more extensive possibilities compared to the classic editor TinyMCE.

Define best image sizes in WordPress post/page ensures accessibility. Source of the image used: ESB Professional/shutterstock.com“)

If you want to save your custom settings for later reuse, you can use the Gutenberg “Add to reusable blocks” section and also lock it against accidental modification. This is a huge labor saver if you frequently publish new posts.

For profession-specific sites, such as a photographer’s website, additional image formats may be needed to perfectly represent your vision. Our guide “compress images” gives further help to adjust image sizes, e.g. for WordPress gallery plugins.

Tip

WordPress lazy loading is another way to improve website loading times. In this case, images are loaded only when they enter the visible area while scrolling the web page.

Disable WordPress default sizes for images

The easiest way to disable the default image sizes is to use the “Disable Media Sizes” plugin. In its settings, all seven generated image formats are also listed.

Disable preset image sizes in WordPress using a plugin
The “Disable Media Sizes” plugin allows you to disable the generation of preset WordPress image sizes

With the plugin settings shown, the deselected formats are not generated at all. The upload of the original image cannot be “switched off”. This is an advantage if you want to generate other formats later after all.

Note

Adding further image formats or suppressing them is also possible with entries in the WordPress core files functions.php and index.php. However, this should be reserved for experienced programmers. A first overview of the programming language can be found in our PHP beginner tutorial.

Further optimize images for WordPress with plugins

In practice, images are mainly used as JPG and PNG. The file sizes of these image formats can be further adjusted with image editing programs. In Photoshop, there is a query for quality when saving or exporting. The disadvantage of this method is that each image must be “touched” individually and then uploaded. Plug-ins are a more elegant solution. These often have a wide range of functions, so a close look at the documentation of the plugin used is advisable.

High installation numbers and good ratings have, for example, the following WordPress plugins for adjusting WordPress file and image sizes:

  • EWWW Image Optimizer: Supports the formats: JPG, PNG, GIF, PDF, WebP, SVG
  • TinyPNG: Supports JPG, PNG, WebP
  • Imagify: Supports JPG, PNG, PDF, GIF, WebP
  • Regenerate Thumbnails: not updated for some time now
  • Image Regenerate & Select Crop: likewise

Remember before trying plugins: A WordPress backup protects against data loss if something really goes wrong.

Summary: Optimize WordPress image sizes

With the on-board tools of WordPress, many optimal image sizes can already be achieved. With plugins more extensive possibilities are available. The intervention in the PHP code of a WordPress site should be reserved for programming professionals. And finally: Keep the image SEO in mind when optimizing.

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