How to Fix "Serve Images in Next-Gen Formats" in Google PageSpeed Insights
You ran your site through Google PageSpeed Insights for the first time. You were hoping for a clean green score. Instead, you got a wall of red and orange warnings — and sitting right near the top of the list is this one: "Serve images in next-gen formats." Don't panic. This is one of the most common PageSpeed warnings on the entire internet, and it is also one of the easiest to fix.
In this guide, we'll break down exactly what this warning means, why Google cares about it so much, and the precise steps you can take today to make it disappear — without touching a single line of code.
What Does "Serve Images in Next-Gen Formats" Actually Mean?
When Google flags this warning, it is telling you one simple thing: your images are using old formats — typically JPEG or PNG — and you could be using a newer, far more efficient format instead. The formats Google specifically recommends are:
- WebP — Developed by Google itself. Typically 25–35% smaller than JPEG at the same visual quality.
- AVIF — Even newer than WebP. Can be up to 50% smaller than JPEG, though browser support is still catching up.
Think of it like this. You're shipping packages with a courier that uses large, old vans. Google is pointing to a newer fleet right outside the door and saying: "Those vans hold twice as much and arrive twice as fast — why aren't you using them?" The warning isn't saying your images look bad. It's saying your images are heavier than they need to be.
Why Google Penalises Old Image Formats in 2026
Google's ranking algorithm uses a set of performance metrics called Core Web Vitals. The one most affected by heavy images is Largest Contentful Paint (LCP) — which measures how long it takes for the biggest visible element on the page (usually a hero image or banner) to fully load. A slow LCP is a direct ranking penalty.
Here is the reality: a standard homepage hero image saved as JPEG at full resolution might be 400KB. The exact same image saved as WebP, at identical visual quality, comes in at around 270KB. That is 130KB less data the user's phone has to download before they see anything. On a 4G connection with average signal — which is how most mobile users experience your site — that difference is felt.
Step-by-Step: How to Fix the Warning
There are two main ways to fix this depending on whether you run a simple website or use a CMS like WordPress.
1Identify Which Images Are Causing the Warning
Go to pagespeed.web.dev, enter your URL and run the test. Under the "Opportunities" section, click on "Serve images in next-gen formats." PageSpeed will show you a list of every image on your page that is still in an old format, along with the estimated file size savings for each one. Screenshot or note down those filenames — these are the ones you need to convert.
2Convert Your Images to WebP
This is the practical step. Take each flagged image and convert it to WebP. You don't need Photoshop or any installed software. Simply use a browser-based tool — upload your JPEG or PNG, select WebP as the output format, and download the converted file. The entire process takes under a minute per image. For most sites, you'll have all your images converted in under 15 minutes.
3Replace the Old Images on Your Site
Upload your new WebP files to wherever your images are hosted. Then update the image references in your HTML or CMS to point to the new files. If you're on WordPress, plugins like ShortPixel or Imagify can automate this — but converting manually with a dedicated tool gives you more control over quality and naming.
4Re-run PageSpeed and Verify
Once your new WebP images are live, head back to PageSpeed Insights and run the test again. In most cases, the "Serve images in next-gen formats" warning will be gone or significantly reduced. You should also see a measurable improvement in your LCP score and overall Performance score.
WebP vs JPEG vs PNG: A Quick Size Comparison
To put the savings in concrete terms, here is a real-world comparison of the same photograph saved in three formats at equivalent visual quality:
| Format | File Size | Transparency | PageSpeed Safe? |
|---|---|---|---|
| JPEG | ~380 KB | No | ❌ Flagged |
| PNG | ~620 KB | Yes | ❌ Flagged |
| WebP | ~245 KB | Yes | ✅ Recommended |
The numbers speak for themselves. By switching from PNG to WebP, you can reduce a single image's file size by 60% or more — while keeping the same visual quality and even retaining transparency support.
What About Browser Support for WebP?
This used to be a legitimate concern back in 2020 when Safari didn't fully support WebP. In 2026, that concern is essentially gone. WebP is now supported by over 97% of all browsers worldwide, including every version of Chrome, Firefox, Safari, Edge, and mobile browsers. Unless you are specifically targeting users on Internet Explorer (which itself has been discontinued), you can use WebP without any fallback worries.
Common Mistakes People Make When Fixing This Warning
- Converting but not replacing: Some people convert their images to WebP but forget to update the image source links in their HTML or CMS. The old JPEG is still loading. Always double-check that your page is actually serving the new file.
- Using a low-quality conversion: Not all conversion tools are equal. Some free tools compress aggressively and produce blurry WebP files. Always preview the output before replacing your originals.
- Ignoring images in CSS: Background images defined in your CSS file using
background-image: url()are also scanned by PageSpeed. Don't forget to convert those too. - Only fixing the homepage: PageSpeed tests one URL at a time. Your blog posts, product pages, and landing pages may each have their own set of flagged images. Spot-check your highest-traffic pages individually.
Fix the Warning in Minutes
Convert your JPEG and PNG images to WebP instantly — directly in your browser. No account needed, no uploads to any server, completely free.
The Bigger Picture: One Fix, Multiple Benefits
Fixing this PageSpeed warning is not just about ticking a box on an audit report. Every image you convert to WebP makes your site faster for real users on real connections. Faster sites rank higher on Google, hold visitors' attention longer, and convert better. A single afternoon spent converting your image library could improve your search rankings, reduce your bandwidth costs, and make every page feel snappier — all at the same time.
Start with the images that PageSpeed flags as having the highest potential savings. Convert them to WebP, replace them on your site, and re-run the test. Most sites can clear this warning in under an hour. Your score will thank you.