How to Fix Wrong-Sized Images in WordPress

One of the things that often confuses people new to WordPress is how it handles images. WordPress automatically keeps track of your images. Set them as featured, add them to posts, all that good stuff. It’s pretty cool when you discover this power. But then something happens: you switch themes, update a plugin, or change your site’s layout, and suddenly all your images look wrong. They’re not the right size, or they’re fuzzy, or they’re just… off.

This can show up in different ways depending on your situation. Here are the common symptoms:

• You’re seeing full-size images where you expected smaller, optimized versions
• Images appear too small or fuzzy in places where they should look crisp
• New images look perfect, but older images seem a little “off”

If any of these sound familiar, you need to regenerate your image thumbnails.

Why This Happens

Here’s what’s going on: when you upload an image to WordPress, it automatically creates multiple sizes based on your theme’s requirements. But when you switch themes, install certain plugins, or change your site layout, you might need image sizes that WordPress didn’t create when you first uploaded those images. Your old images are still stuck with the old sizes.

That’s where the Regenerate Thumbnails plugin comes in.

The Solution: Regenerate Thumbnails

Regenerate Thumbnails is a free plugin that fixes your WordPress image library by recreating all the image sizes your site currently needs. It doesn’t harm your original images. It just generates new thumbnail and intermediate sizes as if you’d uploaded everything fresh with your current settings.

Modern WordPress is pretty smart about generating responsive image sizes automatically. But theme changes, new image size requirements, or even switching to WebP format can still leave you with mismatched sizes. That’s exactly what this plugin solves.

Pro tip: If you have a massive image library (thousands of images), consider regenerating thumbnails on a staging site first. You can also use WP-CLI if you’re comfortable with command line tools. It’s faster and won’t tie up your browser.

Step-by-Step: How to Regenerate Thumbnails

1. Install and Activate the Plugin – Go to Plugins > Add New in your WordPress dashboard’s left sidebar. Search for “Regenerate Thumbnails” and click the Install button on the result. Once it’s installed, click Activate.

2. Find the Plugin Settings – Navigate to Tools > Regenerate Thumbnails.

3. Start the Regeneration Process – On the page, click the button to Regenerate Thumbnails For All X Attachments. This will start the plugin working through your image library. Keep this browser tab open while it runs. How long this takes varies dramatically depending on your image library size. Anywhere from a few seconds for small sites to 15 or 20 minutes for larger ones.

4. You’re Done! – When the process completes, all your images should display at the correct sizes. The plugin provides a nice report showing what it did and any errors it encountered. Errors are rare though.

That’s it! Your images should now look as expected across your entire site. Onto solving the next WordPress puzzle!