Image Weight Audit

What this tool does

It reads one page, finds every image on it, and asks each file how much it weighs. Then it takes the biggest ones, converts them to AVIF and WebP, and tells you what came back.

That last part is what makes it worth running. “Consider a modern format” is advice you can read anywhere. “This file is 402 KB, and 6 KB as AVIF” is a number about your image, and we got it by actually converting the thing.

Findings come back as a short list of what to do, biggest first, rather than a pile of measurements. A single 7 MB file and forty small ones are very different problems, and the list says which one you have.

How to use it

1. Paste the URL of a single page. The homepage is the obvious first run, though a product or category page usually tells you more.
2. Read the short version at the top. If your total is under about 500 KB, everything below it is housekeeping and you can stop there.
3. Work down the fix list. It’s ordered by what you get back, so the first item is the one worth doing today.
4. Open the table at the bottom if you want the detail on every file — original weight, converted weight, dimensions, and what we flagged.

Animated GIFs get their own line, because on a page that has them they’re usually the heaviest thing on it, and converting them to a newer image format is the wrong fix. A GIF saves every frame at almost full size. The answer is a video file.

How it works

We fetch the page on our server and read it for images. Every image we find gets weighed from its response headers, which is quick enough to do for all of them.

The biggest files that can be improved are then downloaded and converted twice — AVIF at quality 50, WebP at quality 80 — and whichever comes back smaller is what you see. Images under 20 KB are skipped, because the saving isn’t worth the trip. SVGs and animations get weighed but never converted.

Two limits worth knowing. It reads the page’s code, so an image set by styling or added by a script is invisible to it. And working out which image Google actually times needs a real browser, so we treat the first image on the page as a stand-in — right often enough to be useful, wrong often enough that we’d rather say so.

Image weight is one part of Site Speed, where we break down LCP — the metric these files affect most. And for everything else a page might be getting wrong, the Site Audit covers far more ground than one check can.