Table of contents
Basic image sizesBasic image size usesChange default sizesAdd custom image sizesRegenerate thumbnails after changesHow to resize imagesTheme and plugin image sizesResponsive imagesOptimizing for speedTroubleshootingBest practices
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WordPress Guide → Images → Size

WordPress image sizes: A complete guide [2026]

wordpress image sizes

Image sizes can make or break your WordPress site—visually and technically. Whether you’re running a blog, portfolio, or ecommerce store, knowing how WordPress handles images will help you deliver a better experience and a faster site.

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What are WordPress image sizes?

When you upload an image to WordPress, it automatically generates multiple versions of that image in different sizes. These are used across various parts of your site to optimize layout and performance.

  • Thumbnail: Typically 150×150 pixels. Used in galleries, blog archives, and related post sections.
  • Medium: Up to 300×300 pixels. Commonly used inside post content.
  • Large: Up to 1024×1024 pixels. Good for featured images or wide content areas.
  • Full: The original image size you uploaded.

These sizes help WordPress serve the right image based on where it appears and what device the visitor is using.

Default WordPress image sizes explained

Each default size has its role:

  • Thumbnail: Square crop, used for previews and grids.
  • Medium: Fits comfortably in most blog post layouts.
  • Large: Ideal for banners or large sections.
  • Full size: Only use when you need the original, high-resolution version.

You can choose which size to insert into posts or pages, and WordPress themes often reference these sizes automatically in templates.

How to change default image sizes

You might want to change the default image sizes in WordPress to better match your theme’s layout and design requirements. It also helps prevent unnecessary image cropping or distortion, while improving site performance by avoiding oversized images.

You can update the default sizes in two main ways:

Changing sizes in WordPress settings

  1. Go to Settings > Media in your dashboard.
  2. Change the width and height values for thumbnail, medium, and large.
  3. Save changes.

Note: Changing these values only affects future uploads. Existing images won’t be resized.

Using functions.php or a custom plugin

If you’re building a custom theme or want more control:

update_option(‘thumbnail_size_w’, 300);
update_option(‘thumbnail_size_h’, 300);

Use a child theme to make sure your changes don’t get overwritten by updates. After changing these values, you’ll need to regenerate your thumbnails.

How to add custom image sizes

Adding custom image sizes gives you more control over how images appear in specific areas of your site, like featured sections, sliders, or custom post types. It ensures consistent dimensions across your layout without relying on manual resizing or CSS adjustments.

You can define additional sizes with add_image_size() in your theme’s functions.php file:

add_image_size( ‘custom-thumb’, 600, 400, true );

The last argument (true) enables hard cropping. You can then use this custom size in your templates:

the_post_thumbnail(‘custom-thumb’);

How to regenerate thumbnails after changes

When you change image sizes or add new ones, old images need to be resized to match. The easiest way to do this is with a plugin. Force Regenerate Thumbnails, for example, lets you delete all old image sizes and regenerate thumbnails for your media library based on your current image size settings.

This step is essential to make sure all image sizes are available for your existing content.

How to resize images in WordPress

You might need to resize an image in WordPress to improve page load speed, ensure it fits your theme’s layout, or fix issues with blurry or distorted visuals. Resizing also helps reduce storage usage and makes your media library more efficient.

Here are your options:

Resize before uploading (recommended)

  • Use tools like Photoshop, GIMP, or Canva to size images to exact pixel dimensions.
  • Upload images at 2x the display size for Retina-ready sharpness.

Resize in the WordPress Media Library

  1. Go to Media > Library.
  2. Click an image, then click Edit Image.
  3. Under Scale Image, enter new dimensions and click Scale.

Note: This changes the original full-size image, so back it up if needed.

Resize using a plugin

  1. Imsanity: Auto-resizes large uploads.
  2. Resize Image After Upload: Replaces the original with a resized version.
  3. EWWW Image Optimizer: Handles both resizing and compression.

These plugins are helpful for keeping file sizes under control, especially on multi-author sites.

WordPress theme and plugin image sizes

Some themes and plugins register their own image sizes.

  • WooCommerce uses product-specific sizes.
  • Page builders like Elementor add their own presets.

You can disable unused sizes with the intermediate_image_sizes_advanced filter to save storage.

Responsive images and srcset in WordPress

A responsive image automatically adjusts its size and resolution to fit different screen sizes and device types, like desktops, tablets, and smartphones. In WordPress, this is handled using srcset and sizes attributes, which let the browser choose the best image version to load based on the user’s screen.

You might want to customize responsive image behavior to control which image sizes load on different devices, reduce bandwidth for mobile users, or fix layout issues caused by automatic scaling. It also gives you more flexibility in design and performance optimization, especially if your theme uses non-standard breakpoints or custom image placements.

You can customize how WordPress generates these values using filters like wp_calculate_image_srcset. Lazy loading is also enabled by default since WordPress 5.5.

Optimizing WordPress image sizes for speed

Optimizing WordPress image sizes for speed helps your site load faster, which improves user experience, boosts SEO rankings, and reduces bounce rates. Smaller, properly sized images also save server resources and bandwidth, especially important for high-traffic sites or mobile users.

To keep your site fast:

  • Upload images at the right dimensions
  • Compress images before or after uploading
  • Use next-gen formats like WebP or AVIF
  • Only use full-size images when truly needed

Top plugins for optimizing images and image sizes on WordPress:

These tools automate compression, conversion, and even lazy loading.

Image size troubleshooting

Common issues and fixes:

  • Images appear blurry: This usually happens when a small image is scaled up beyond its actual resolution. Fix it by uploading a higher resolution image that matches or exceeds the display size.
  • Wrong size loading: Your theme may be calling the incorrect image size or not using the srcset attribute properly. Check your theme templates and use the_post_thumbnail() with the correct size name.
  • Old images don’t match new sizes: WordPress doesn’t automatically regenerate images when you change size settings; use a plugin to fix this. Run Regenerate Thumbnails to recreate the necessary sizes.
  • Too many sizes created: Some themes and plugins generate extra sizes you might not need, which takes up storage space. Disable unused image sizes using the intermediate_image_sizes_advanced filter in your theme.
  • Library clutter: Over time, unused images and sizes accumulate; clean them up with a media management plugin. Use a tool like Media Cleaner to identify and delete files no longer used in your content or templates.

Best practices for WordPress image sizes in 2026

  • Upload images in dimensions close to where they’ll be displayed.
  • Compress and convert images to WebP or AVIF.
  • Use consistent aspect ratios across your theme.
  • Only register and keep image sizes your theme actually uses.
  • Regularly clean up unused or outdated media files.

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