WordPress Image Sizes — Featured, Thumbnail, Header & og:image

WordPress Featured Image Size

There is no such thing as “the” WordPress featured image size. Core ships add_theme_support( ‘post-thumbnails’ ), which switches the feature on without defining a single pixel dimension. Your theme picks the size by calling set_post_thumbnail_size( $width, $height, $crop ) — so the correct answer for your site lives in your theme, not in a spec sheet.

That leaves you one practical decision. The featured image is usually the image that gets shared, so sizing it to 1200x630 (1.91:1) makes it work as both the post hero and the social preview. It comfortably exceeds every core sub-size except the 2x ones, so WordPress can still generate sharp retina variants from it.

Resize an image to 1200x630 → Pick the “Featured Image / og:image” preset in the WordPress platform.

WordPress Thumbnail Size

The WordPress thumbnail is 150x150 pixels, and it is the one core size that is cropped to those exact dimensions rather than scaled to fit. That is the thumbnail_cropoption, which defaults to on. Every other core size is a bounding box: a 300x300 “medium” version of a 3:2 photo is actually 300x200.

The practical consequence is that thumbnails are the only place WordPress will cut off part of your image. A wide photo becomes a centered square, so anything important near the left or right edge disappears. You can change all three sizes under Settings → Media — but note that changing them only affects images uploaded afterwards.

Crop an image to 150x150 → Pick the “Thumbnail (cropped)” preset in the WordPress platform.

The Sizes Settings → Media Doesn’t Show You

Settings → Media lists three sizes. WordPress actually registers six. The three missing ones exist to fill the responsive srcset that core writes into every image tag, and you cannot configure them from the admin screen:

This is the real argument for uploading generously: the sub-sizes WordPress can build are capped by the source you give it. A 1000 px wide upload silently skips both retina sizes.

The 2560px Ceiling (and the -scaled File)

Upload an image longer than 2560 pixels on either edge and WordPress will quietly scale it down. Your original is kept, but the file the site serves is a new one with -scaled appended to its name. This is the big_image_size_threshold, and it has been core behaviour since WordPress 5.3.

It surprises people who upload a 4000 px photo and then find photo-scaled.jpg in their media library. Nothing is broken — but it does mean there is no point uploading beyond 2560 px unless you have raised the threshold with a filter.

Resize an image to 2560x2560 → Pick the “Max Upload Before Scaling” preset in the WordPress platform.

WordPress Header Image Size

Like the featured image, the header has no core dimension. When a theme calls add_theme_support( ‘custom-header’ ) without arguments, core defaults to width => 0, height => 0 — literally unset. The theme supplies the numbers, and the Customizer then tells you what they are.

So the way to find your header size is to look, not to guess: open Appearance → Customize → Header Image, and WordPress states the size the active theme expects, along with whether it will let you crop or use a flexible height.

WordPress og:image Size

WordPress core does not output an og:image tag at all. If your posts show a preview image when shared, an SEO plugin is adding it — and the size it should be comes from the platforms doing the rendering, not from WordPress.

Meta’s sharing documentation is the one to build against: use an image of at least 1200x630 pixels, keep it as close to 1.91:1 as you can so it renders in Feed without cropping, and stay under the 8 MB file-size limit. The minimum allowed dimension is 200x200. Note the height is 630, not 628— the 628 figure is repeated widely but it is not the number in Meta’s image guidelines.

Resize an image to 1200x630 → Pick the “Featured Image / og:image” preset in the WordPress platform.