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PageSpeed Insights says to serve images in next-gen formats. How do I fix it?

Re-encode the images the report lists as WebP with the compressor, compare the saving in the table, then replace the files on your site and update their links. The finding asks for modern formats such as WebP instead of JPEG and PNG. Measurement shows, though, that on some images the saving comes from the format and on others mostly from the quality setting, so go by the numbers, not the format name.

Published · 3 min read

What the report is actually saying

PageSpeed Insights, which runs on Lighthouse, lists images that could be smaller in a newer format, along with an estimate of the kilobytes you could save. The name of this finding and how it is grouped have changed between report versions, so in newer versions you may find it inside a broader item about improving image delivery. Either way, the list of images it names is your starting point.

What the numbers say

Worked example

Two images converted to WebP at quality 75 in Chrome:

A photographic 640×480 PNG of 271.3 KB became 21.8 KB, 92% smaller. Here the format alone made the difference.

A 1600×1200 JPEG of 689.5 KB became 203.8 KB as WebP, but 201.5 KB as JPEG at the same quality.

For the second image, nearly all the saving came from re-encoding at a sensible quality, not from the format. Swapping in a WebP file may clear the format finding from the report, but the real benefit to visitors is the smaller size, and you can get that with either format.

How to carry it out

  1. Copy the image names from the report and get their originals from your computer or your site files.
  2. Add them to the Image compressor, choose WebP, and start at quality 75 or 80.
  3. Check the Change column and the preview, especially for images with text or a logo.
  4. Download the files. Their extension is now .webp, so update the links to them in your pages or theme, or upload them through your platform's dashboard in place of the old ones.
  5. Run the report again and confirm the images are no longer listed.

What this tool does not solve

  • If the report also flags images that are larger in pixels than the space they are shown in, the fix is resizing, not compressing. The compressor keeps dimensions as they are, so use the image resizer for that.
  • The tool does not change your website or upload anything to it. It prepares files on your device, and replacing them is a step you take.
  • If some places cannot take WebP, such as email templates or third-party platforms, keep a JPEG version for them. To convert file formats for other purposes, use the Image format converter.

Common questions

Can the tool produce AVIF?

No. It outputs JPEG or WebP only.

Will WebP improve my search ranking?

We make no such promise. Lighter images make the page faster for visitors, which is a direct benefit whatever else happens.

Is the saving the report estimates what I will actually get?

The report estimates; the tool measures. Go by the figure the tool shows for your files.