Image Size Checker
Free, no sign-up: enter a URL and we load up to 40 images from the page and show each one’s file size, real format (from the file’s contents, not its extension), pixel dimensions versus the size set in HTML, lazy loading and alt — then tell you what to compress, resize or convert to WebP/AVIF. Check your own files in the “My files” tab, right in your browser with no upload.
Rendered size on screen
A server cannot see the size a browser actually draws an image at. Open your page, press F12 → Console and paste the line below to get a table of intrinsic size, rendered size and how many times too large each image is.
console.table([...document.images].filter(i=>i.naturalWidth).map(i=>({src:(i.currentSrc||i.src).split('/').pop().slice(0,60),intrinsic:i.naturalWidth+'×'+i.naturalHeight,rendered:i.clientWidth+'×'+i.clientHeight,dpr:devicePixelRatio,xTooBig:+(i.naturalWidth/Math.max(1,i.clientWidth*devicePixelRatio)).toFixed(1)})).sort((a,b)=>b.xTooBig-a.xTooBig))
Key facts
- Price
- Free
- Sign-up
- Not required
- Processing
- URL mode runs on our server: the page and up to 40 images are fetched through SSRF protection and not stored; “My files” runs only in your browser
- Input
- A page URL (<img> images, up to 8 MB per file) or your own image files
- Limits
- URL mode: 6 checks a minute; 15 a day without an account, 45 with one, unlimited with Pro; “My files” is unlimited
- Output
- For each image: format from file contents, pixels, file size, HTML size, srcset, lazy loading, alt and tips; total weight and estimated savings
- Last updated
Alternatives
Other tools for the same job, and what each one does well:
- PageSpeed Insights — Renders the page and its Lighthouse audits count wasted image bytes precisely (sizing, format, compression).
- Squoosh — Google’s in-browser app for compressing and converting a single image with a quality preview (WebP, AVIF and more).
When to choose this tool: When you want a quick overview of every image on a page — real format, pixels, weight and what is excessive — without signing up, or need to check your files before uploading them.
Descriptions checked against each tool's own site in October 2026.
Free Image Size Checker
Images are usually the heaviest part of a page, and the problem is rarely how many there are — it is a 4000 px photo shown in a 400 px slot, or a PNG where WebP would do. The tool downloads up to 40 images from a page and shows each one’s real format (from the file contents), pixel dimensions, file size and the size set in HTML, flags lazy loading, srcset and alt, and explains what to fix: resize, compress, convert to WebP or AVIF, replace a GIF with video, add width and height. In the “My files” tab you can check the size and weight of your own images right in your browser without uploading anything.
How to Use
- Enter a page URL or open the “My files” tab
- Sort images by weight and start with the heaviest
- Resize and compress, then check the page again
FAQ
The three “sizes” of an image
| What | Where to look | Why it matters |
|---|---|---|
| File size (KB, MB) | the “Size” column | What visitors download — the key to speed |
| Pixel dimensions | the “Pixels” column | How detailed the image is; extra pixels mean extra weight |
| Size on screen | width/height in the “HTML” column, plus the console snippet | How many pixels the page actually needs |
Rule of thumb: the file should be no wider than twice its display size (for 2× screens). A 4000 px photo in a 400 px column weighs dozens of times more than needed.
Which format to use
- WebP — Google’s data shows it is 25–34% smaller than JPEG at similar quality; every modern browser supports it.
- AVIF — often smaller still, but slower to encode; good for large photos.
- JPEG — the fallback for photos; quality 75–85 usually looks the same as 100.
- PNG — for screenshots, diagrams and transparency; too heavy for photos.
- SVG — for logos and icons; run it through an optimiser if it is more than a few KB.
- Animated GIF — replace it with an MP4 or WebM video using
autoplay muted loop playsinline; the file becomes many times smaller.
We detect the format from the file contents: sometimes photo.jpg is really WebP because a CDN converts it on the fly — that is fine.
srcset: different files for different screens
A srcset list of widths plus sizes lets a phone download a small file and a large monitor a big one:
<img src="photo-800.webp"
srcset="photo-400.webp 400w, photo-800.webp 800w, photo-1600.webp 1600w"
sizes="(max-width: 600px) 100vw, 800px"
width="800" height="533" alt="…" loading="lazy">
Most CMSs create these copies automatically — make sure your theme outputs srcset.
Optimisation order
- Sort the table by weight and start with the 3–5 heaviest files — they are usually half the total.
- Resize oversized images to twice their display size.
- Convert JPEG and PNG to WebP or AVIF (image converter, image compressor).
- Add
widthandheightto every image to prevent layout shifts (CLS). - Use
loading="lazy"below the fold, but not on the main image at the top — give that onefetchpriority="high". - Re-check here and with the page speed test.
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