How to Convert JPG to WebP for WordPress (And Actually Improve Your Site Speed)

WebP is Google's image format. It supports both lossy and lossless compression, transparency, and animation — essentially replacing JPG, PNG, and GIF in one format. The important number: WebP files are typically 25-35% smaller than JPG at the same visible quality. On a photo-heavy blog post, that's the difference between a 3 MB page and a 2 MB page. On a homepage with a hero image, it's the difference between passing and failing the LCP threshold.

Every mainstream browser has supported WebP since 2020. If your audience is on anything modern (Chrome, Firefox, Safari 14+, Edge), WebP just works — no fallback needed for the majority.

Start with the images you're about to upload. Drop them into the JPG to WebP converter, keep the default 85% quality (a good sweet spot), download the results. If you've got the batch of a WooCommerce product catalogue, load up to 20 at once — the filenames come through with the new .webp extension so replacement is straightforward.

By default, WordPress refuses WebP uploads until version 5.8+. If you're on 5.8 or later, you're fine — drop the WebP into your media library like any other image. If you're on an older WordPress, you'll see a "Sorry, this file type is not permitted" error.

Two ways around it:

• Update WordPress. If you're running 5.7 or older in 2026, the security updates alone are worth it.
• Install a plugin. WebP Express or Imagify both add WebP support. WebP Express also serves WebP automatically to browsers that support it, keeping the original JPG as a fallback.

Some older themes hardcode image extensions in their CSS or PHP — expecting .jpg or .png. Uploading a .webp with the same base filename replaces the reference, but if the theme is looking for "hero.jpg" specifically, the WebP won't show. Test on staging first, always.

Newer block themes handle this cleanly. Older themes (especially bespoke custom themes) may need CSS tweaks.

Depends on the scale.

For a small site (under 100 images): convert everything. The Site Health improvement is worth the afternoon.

For a large site (thousands of images): use a plugin like ShortPixel or Imagify to bulk-convert your media library in place. They keep the originals as fallbacks and serve WebP where supported. Manual conversion of thousands of files is a bad use of your time.

For an e-commerce store: prioritise category pages and top-selling products first. Those pages have the highest traffic and Core Web Vitals impact.

After the switch, run one of your important pages through PageSpeed Insights and check the LCP (Largest Contentful Paint) score. On a hero-image-heavy landing page, converting the hero JPG to WebP typically shaves 0.3-0.6 seconds off LCP. That's usually enough to move you from "Needs Improvement" to "Good" in the Core Web Vitals report.

Google's Search Console also reports Core Web Vitals field data. Give it 2-3 weeks after the change to see updated real-user metrics.

Convert new images to WebP before uploading. Bulk-convert existing media with a plugin if the site is large. Update WordPress or add a WebP plugin if you're on an old version. Test on staging first if the theme is custom. The bandwidth savings pay for themselves — faster pages, better Core Web Vitals, happier users.