You added a few beautiful photos to your site, and ever since, pages take forever to load? This is one of the most common scenarios on WordPress: images taken straight from a smartphone or downloaded in high definition, never resized, each weighing several megabytes. Optimising WordPress images is often the fastest performance lever to put in place.

Converting your images to WebP and resizing them correctly can cut their weight by three, with no visible loss of quality to the naked eye. On a site where images typically make up half the total weight of a page, the gain in loading time is immediate.

In this article, we explain why images are so often the cause of a slow site, what the WebP format really brings, and how to set up lasting optimisation without spending your evenings on it.

Why images so often weigh down a WordPress site

A photo taken with a recent camera or a high-end smartphone easily reaches 4 to 8 megabytes, at a resolution far higher than what actually shows on screen. Yet most WordPress sites display their images at a much more modest size, sometimes 800 or 1200 pixels wide.

Sending a 4000-pixel-wide image to display it at 800 pixels means making every visitor download a file five times heavier than it needs to be. Multiply that waste across a dozen images on a homepage or portfolio page, and you get loading times that hurt both user experience and search rankings.

Image format also plays an important role: JPEG and PNG, while widespread, are far from the most efficient formats for web compression.

What the WebP format actually changes

WebP is an image format developed for the web that offers markedly better compression than JPEG and PNG at equivalent visual quality. Concretely:

  • A typical JPEG photo can lose 25 to 35% of its weight in WebP, with no visible difference.
  • An image with transparency (logo, icon) gains even more compared to a PNG.
  • The format is supported by all modern browsers, which removes the old barrier to adopting it.

This is not a marginal option: it is now the default recommended format for any image published on a WordPress site, except in very specific cases (an image needing complex transparency combined with animation, for example).

Resize before you compress

Converting to WebP is not enough if the original image is already oversized. The first rule of optimisation remains resizing the image to the size it will actually be displayed at, even before thinking about format.

Concretely, this means:

  • Identifying the maximum display width for each spot (banner, thumbnail, gallery).
  • Resizing the source image to that width, with a reasonable margin for high pixel-density screens.
  • Never uploading a "raw" photo straight out of a camera without resizing it first.

WordPress automatically generates several sizes for each uploaded image, but this does not replace resizing beforehand: the original file, often very heavy, stays stored and can be served by mistake if the theme or a plugin doesn't target the right size.

Automating optimisation with a plugin

Redoing this optimisation manually for every image quickly becomes tedious, especially on a site with a product catalogue or a large media library. Several WordPress plugins automate this work:

  • They automatically convert uploaded images to WebP (keeping a JPEG version for compatibility if needed).
  • They compress images with no perceptible loss of quality.
  • Some also offer to bulk-reprocess the entire existing media library.

Automation becomes essential as soon as the site is updated regularly, since it guarantees every new image follows best practice without manual work on each publish.

Lazy loading, an essential complement

Beyond format and size, lazy loading avoids loading every image on a page as soon as it opens, loading only the ones visible on screen while the rest load as the visitor scrolls. WordPress has built this in natively for several versions now, but it's worth checking it works correctly, particularly for images right at the top of the page (which should never be deferred, or the initial display will be slowed down).

The direct impact on speed and SEO

Image weight is usually the first factor that drags down performance scores measured by tools like Google PageSpeed Insights. Reducing that weight directly improves LCP (the loading time of the main page element), a criterion Google now factors into its search result rankings.

On a site that is already slow for other reasons (hosting, no cache, too many plugins), optimising images alone won't fix everything. Our page on a slow WordPress site covers the full range of possible causes, and our article on WordPress cache usefully complements image work for a site that's fast from end to end.

When to call in a professional

Optimising a few images now and then is within anyone's reach. But reprocessing a media library of hundreds or thousands of images, checking that lazy loading doesn't break any layout, or diagnosing why a page stays slow despite optimised images requires technical expertise and time.

A professional can also spot the edge cases where automation alone isn't enough, for example images generated dynamically by a third-party plugin that slip past standard processing.

Frequently asked questions

Does the WebP format work on every browser? Yes, all modern browsers (Chrome, Firefox, Safari, Edge) have supported it for several years now. The rare cases of older compatibility are handled automatically by plugins that offer a fallback format.

Should you delete the original images after converting to WebP? No, it's best to keep source files in a non-public location, in case a future edit is needed. Only the versions served to visitors need to be optimised.

How much weight can you really save on a page? It depends on the starting point, but it's not uncommon to cut the total weight of an image-heavy page by two or three after full optimisation (resizing, WebP conversion, compression).

Is your site being slowed down by heavy images and you don't know where to start? The Relax by Yumea team audits your pages for free and identifies the priority optimisations. Request your free diagnosis with Relax by Yumea.