PageSpeed Flagged One 105 KB Image: How We Cut It by 85% on Mobile

PageSpeed Insights flagged a single image on our homepage: a 105 KB screenshot, with an estimated 88 KB of it wasted. One image, one warning, and it was right. The file was 1440 pixels wide and phones were downloading all of it to show a picture about 400 pixels across.

The fix took about twenty minutes and cut the download on a phone from 108 KB to 16 KB. Here is what was wrong, what we changed, and the numbers, because this exact problem sits on most WordPress sites. For the wider picture beyond images, see our WordPress speed optimization guide.

Written for site owners who see this warning and do not know what to do with it, by Jasper Frumau, WordPress developer at Imagewize, based in the EU. Last updated October 27, 2026.

What PageSpeed actually said

The report listed one file under image delivery: a screenshot of a WooCommerce product page with the EU legal guarantee notice open. It showed 105.2 KiB transferred and an estimated saving of 88.2 KiB. That second number is the useful one. It says the page could look identical with about 84% fewer bytes.

A 105 KB image is not a disaster on its own. The reason to care is that this was one image among many, on the homepage, loaded by people on phones and mobile data. Every unneeded kilobyte delays the moment the page looks finished, and image weight is one of the easiest speed wins to take.

Three causes, all common

1. Too big for its slot. The file was 1440 by 900 pixels. On the homepage it sat in a card about 400 pixels wide on a phone and under 1000 on a desktop. The extra pixels were downloaded and thrown away.
2. Old format. JPEG is fine for photos, but this was a screenshot with flat colors and sharp text. WebP compresses that kind of image much better at the same visible quality.
3. No smaller versions offered. WordPress creates several sizes of every uploaded image and lets the browser pick the right one, but only when the image is tied to a Media Library entry. Ours was pasted in as a plain file address, so every device got the biggest file.

The third one is the sneaky one. The page looked fine, nothing was broken, and a plugin could not have told you about it. The image simply had no connection to WordPress, so WordPress could not help.

What we changed

1. Cropped to the shape it is shown in. The card shows it as 16:9, so we cut the file to 16:9 and lost nothing visible.
2. Resized to 1000 pixels wide. That is the widest it is ever displayed.
3. Converted to WebP. We checked that the small legal text in the screenshot was still readable.
4. Uploaded it to the Media Library and used that entry. WordPress then generated 300, 768 and 1000 pixel versions and added the list of sizes to the page automatically.

Before and after

These are the measured file sizes served from the live site. We have not yet re-run a full PageSpeed test, and Google’s report lags a few days behind changes, so we are not quoting a new score. The point of this fix is fewer bytes, and bytes are easy to verify. We will update this post once the new test is in.

One exception: keep JPG for the social share image

WebP is the right format for images inside your pages. It is not the safest choice for the picture that appears when someone shares a link on Facebook, LinkedIn or X. Support for WebP in link previews has not always been reliable across platforms, and a broken preview costs more than the 20 KB you would save. So on our site the share image (the featured image, or the social image field in The SEO Framework) stays a JPG, and everything inside the page is WebP.

How to check your own site

• Run your homepage and your top product page through PageSpeed Insights and open the image delivery items. Each lists the file and the bytes it could save.
• Be most suspicious of images that were pasted in as a link or added by a page builder or pattern rather than picked from the Media Library.
• Do not stop at format. A correctly sized JPEG often beats an oversized WebP.

No command line? Tools for Windows and Mac

You do not need a developer’s toolkit to do the first two steps. Any of these works for a one-off image:

Whatever you use, resize first and convert second, then check the result at full size before uploading. Upload it through the Media Library (Media, Add New) and insert it from there, not by pasting a link, so WordPress can create the smaller versions. If you have hundreds of old images, an image plugin that converts and resizes in bulk is a better use of your time than doing them one by one.

magick original.jpg -gravity center -crop 1440x810+0+0 +repage -resize 1000x -strip crop.png
cwebp -q 80 -m 6 crop.png -o image.webp
wp media import image.webp --title="Descriptive title" --alt="Descriptive alt text" --porcelain

for f in *.jpg *.png; do cwebp -q 80 -m 6 "$f" -o "${f%.*}.webp"; done

magick source.png -resize 1200x630^ -gravity center -extent 1200x630 -strip -quality 85 social.jpg

<!-- wp:image {"id":14306,"sizeSlug":"large"} -->
<figure class="wp-block-image size-large"><img src="/app/uploads/2026/10/image.webp" alt="..." class="wp-image-14306"/></figure>
<!-- /wp:image -->

Frequently Asked Questions

• Should I convert all my WordPress images to WebP? Convert images that appear inside your pages and posts, and size them to the slot first. Keep JPG for the featured or social share image so link previews on Facebook, LinkedIn and X stay reliable.
• Why does PageSpeed still flag my image after I converted it to WebP? Usually because the image is still larger than its display size, or because WordPress is not offering smaller versions. Check the pixel size and that the image is used from the Media Library so a srcset is generated.
• How much does one image matter for page speed? One 105 KB image is not the whole story, but images are often among the heaviest parts of a page. Fixing the biggest few can save more than another plugin, and the savings matter most for visitors on mobile data.

Where to go next

• The full picture, from server to browser: WordPress speed optimization: the technical guide.
• The short version for small business sites: WordPress speed optimization checklist.
• Having us do it: WordPress speed optimization service.