Category: WordPress • Est. reading time: 4 minutes
Settings > Media is a small screen with a big job. Every time you add one image to your site, WordPress makes a few resized copies of it behind the scenes, so each page can show the right-sized version instead of loading one oversized file everywhere. Because images are usually the heaviest thing on a page, this screen is really about how quickly your site loads.
What Each Setting Does
Thumbnail size. The size of the little preview image. There is also a box to crop thumbnails to exact dimensions, which keeps grids and photo galleries looking even.
Medium size and Large size. The largest width and height WordPress will use for the medium and large copies. Your image is shrunk to fit inside those limits, never stretched larger.
Organize my uploads into month- and year-based folders. Leave this turned on. It files your images into dated folders instead of piling every upload into one giant heap, which makes them far easier to find later.
The Biggest Speed Win Is Not On This Screen
These settings help, but the single most effective thing you can do is upload images that are already the right size and already compressed before they ever reach WordPress. A photo straight off a phone or camera is often several megabytes and thousands of pixels wide, far bigger than any web page needs, and that extra weight is what slows a page down.
Here is our own rule: we never upload a photo larger than about 1MB, and we shrink it to roughly the biggest size it will actually appear at on the page first. Do that, and your pages stay fast no matter how these settings are configured.
A Few Things Happening Behind the Scenes
Really big images get shrunk automatically. If you upload an image wider than 2,560 pixels, WordPress makes a smaller copy to display and quietly keeps your full-size original too. Add up the original, that smaller copy, and the thumbnail, medium, and large versions, and a single photo becomes several files. Load a lot of big photos and they can slowly fill up your hosting disk space.
WordPress trims image quality a little on upload. By default it saves photos at about 82 percent of full quality. You will not notice the difference on screen, and it makes the files smaller and quicker to load.
Your theme may add its own sizes. On top of the three sizes here, many themes create their own extra sizes for things like sliders and featured images. So this screen is only the part of the picture you control directly.
Advanced: Fine-Tuning (Optional)
If you already prepare and compress your own images, there are a few deeper adjustments you can make. These involve small behind-the-scenes changes, so they are best handled carefully, and we are glad to set them up for you.
Create fewer copies. You can tell WordPress to stop making one or more of the sizes it normally generates, which reduces clutter and saves disk space.
Keep your original quality. If you have already compressed your images yourself, you can switch off the automatic quality trim so WordPress does not compress them a second time.
Keep full resolution. You can turn off the automatic shrinking of very large images if you genuinely need full-size files on the page.
One important caution: only turn off WordPress’s automatic compression or shrinking if you are already optimizing images yourself. Otherwise you will end up with heavier files and slower pages, the exact opposite of what you want.
And whenever you change any of these sizes, the new settings only apply to images you upload afterward. WordPress does not go back and rework the images already in your library, so those keep their old sizes until they are rebuilt, which is a separate step we can take care of.
Our Advice
For most sites, leave these settings at their defaults and keep the month-and-year folders on. Put your effort into uploading right-sized, compressed images instead. That one habit does more for your speed than any setting on this screen.
Want a Hand With This?
Images are one of the biggest reasons websites load slowly. We teach the practical side of images and speed in our live, one-on-one classes at allydrez.com/learn-how-to-use-wordpress, or reach us at support@allydrez.com or 1-321-209-2004.
For a Developer
These add to a child theme’s functions.php. Back up first, and test on staging if you can, since a syntax error here can take the site down. All three affect new uploads only; existing images need to be regenerated afterward.
1. Generate fewer sizes. Set Thumbnail, Medium, and Large to 0 on the Media screen to stop those. To also drop the hidden 768px size and any sizes your theme registers, filter them out by name:
php
add_filter( 'intermediate_image_sizes_advanced', function( $sizes ) {
unset( $sizes['medium_large'] ); // the hidden 768px size
// unset( $sizes['theme-size-name'] ); // repeat for each theme size
return $sizes;
} );2. Keep original quality (stop the ~82% re-compression). Return 100 for both the legacy and current image-editor filters:
php
add_filter( 'jpeg_quality', function() { return 100; } );
add_filter( 'wp_editor_set_quality', function() { return 100; } );3. Keep full resolution (stop the 2560px auto-scaling). Return false to disable it entirely, or return a larger number (e.g. 4000) to raise the limit instead of removing it:
php
add_filter( 'big_image_size_threshold', '__return_false' );