How to Change Featured Image Size in WordPress

Changing the featured image size in WordPress trips people up because the obvious place to look, Settings then Media, does not actually control the featured image. The featured image size is set by your theme, so changing it for real means registering a new size in code and then telling your theme to use it.

I will walk you through the proper way to do it with add_image_size(), when a plugin is the easier route, and the step almost everyone forgets: regenerating thumbnails so your existing images actually update.

First, know what each setting actually controls

The reason this feels confusing is that there are two different things called “image size” in WordPress. Settings then Media controls the three default sizes WordPress generates (thumbnail, medium, large), which your content images use. The featured image, though, is displayed by your theme at whatever size the theme registered, so editing the Media settings often changes nothing visible on your featured images.

If you only want to understand which dimensions to aim for in the first place, I covered that in the companion guide on the featured image size in WordPress. This post is about actually changing it.

Step 1: Register a custom size in functions.php

Add a new image size in your theme’s functions.php (use a child theme so an update does not wipe it). This tells WordPress to generate that size for every new upload. The function is documented in the WordPress developer reference.

add_image_size( 'featured-large', 1200, 675, true );

That last parameter is the one that matters most. With vrai, WordPress hard-crops the image to exactly 1200 by 675, so it always fills the frame but may trim the edges. With faux, it scales the image to fit within those bounds and keeps the original aspect ratio, so nothing is cut but the dimensions are not guaranteed.

Step 2: Display the new size in your template

Registering the size is only half the job; you also have to tell the theme to use it. In a classic theme, find where the featured image is output (often single.php) and pass your new size name to the_post_thumbnail().

the_post_thumbnail( 'featured-large' );

On a modern block theme there is no single.php to edit. Instead, open Appearance then Editor, edit the single-post template, select the Featured Image block, and set its dimensions there. It is the same idea, just done visually rather than in PHP.

Step 3: Regenerate your existing thumbnails

Here is the step people miss. A new registered size only applies to images uploaded after you added it, so your existing featured images will still use their old dimensions. To apply the new size to everything already in your media library, regenerate the thumbnails.

The simplest route is the free Régénérer les vignettes plugin, which rebuilds all sizes in a couple of clicks. If you prefer the command line, wp media regenerate via WP-CLI does the same job without a plugin, which fits nicely if you are keeping the build lean.

Prefer not to touch code?

The code method gives you the most precise control, and I lean on it for client sites. That said, if you are not comfortable editing functions.php, a featured-image or image-size plugin can register and apply a custom size from a settings screen, and for a one-off change that is a perfectly reasonable trade. Just remember it is one more plugin to keep updated, so I only reach for it when code is genuinely off the table.

So what is the cleanest way to change it?

If this were my site, I would register the size with add_image_size(), call it in the template, and then regenerate thumbnails, because that gives a consistent featured size across every post with no extra plugin running in the background. It is three steps, but they are the steps that actually stick.

Reach for a plugin only if editing code is off the table for you, and whichever path you choose, do not skip the regeneration step, since that is the one that makes the change show up on the posts you already published.

---

Share Copier le lien Copier au format Markdown

Want our posts to show up more often on Google?

One step & Google will surface this site in your Top Stories.

Add us as a preferred source on Google

Abdullah Nouman eCommerce SEO, Agentic Commerce SEO & AI Search Specialist

I publish the industry's most critical SEO and AI Search blog, cutting through the hype and explaining what actually holds up in plain English.

Venez travailler avec moi

Lectures complémentaires

Retour à tous les articles →

Réparer les emails manquants de WooCommerce et les renouvellements retardés : Mettre en place un vrai job Cron Un site web WordPress peut-il supporter un trafic de plus d'un million de personnes ? Comment déplacer le badge ReCAPTCHA V3 vers la gauche dans WordPress