What does the rating mean?

A means the file is lean for its format and pixel count, B is good, C is heavier than it needs to be, D is heavy, and F means the file is heavily oversized for its dimensions and format. Aim for A or B for production assets.

What is a good compression score?

80 or above: A is 90 to 100 and B is 80 to 89. C runs from 70 to 79, D from 60 to 69, and anything below 60 is an F. The score comes from bits per pixel, the file size in bits divided by width times height (the first 4 KB of the file is not counted), compared with thresholds for the file's format. For two files of the same format and dimensions, the smaller one never scores lower; lossless WebP counts as its own format here.

Does this actually compress my image?

No, this tool only rates. Use the companion Image Compressor to actually reduce file size. The two together form a pipeline: rate to decide if compression is needed, compress to fix.

Why is my image rated low?

Common causes: PNG used for a photo (JPEG, WebP or AVIF is usually far smaller), a JPEG or WebP saved at a very high quality setting, an unoptimized export from a design tool, or large embedded metadata such as camera EXIF data or a color profile. The grade is per pixel, so it cannot tell whether an image is larger than the size it is displayed at. Check that separately.

Should I use WebP, AVIF, or stick with JPEG?

WebP is the safe default: every current major browser supports it, and Google's WebP documentation puts lossy WebP at 25 to 34% smaller than JPEG at equal SSIM quality. AVIF often compresses further but encodes more slowly and is missing from some older browsers, so serve it with a WebP or JPEG fallback. This tool holds each format to its own thresholds, so a lossy WebP or an AVIF needs fewer bits per pixel than a JPEG to earn the same grade, while a lossless WebP is allowed more.

How does image compression affect Core Web Vitals?

Mostly through Largest Contentful Paint (LCP). When the largest element in view is an image, such as a hero photo, a heavier file takes longer to download and LCP comes later. Cumulative Layout Shift depends on reserving space with width and height attributes, not on file size, and Interaction to Next Paint measures how quickly the page responds to input.

Will compression hurt visual quality?

Lossy compression always discards some detail, but at moderate quality settings the loss is often hard to see. Export at a few quality levels, compare them side by side at the size they will be displayed, and keep the smallest one that still looks right. This tool rates weight per pixel, not visual quality, so check the result with your own eyes.

What if my hero image needs to be high quality?

Use a higher resolution + WebP at quality 85, then serve responsive sizes via srcset. The 4K version exists for retina displays; the 1.5K version serves regular screens. Net page weight stays low because each viewer downloads only the size their device needs.

How do I use this for SEO audits?

Run the hero images of your top organic landing pages through the rater. Treat anything below B as a candidate for compression and fix the highest-traffic pages first. The results double as a quick-wins list for a performance sprint.

Is the file size the only factor?

No. The grade combines file size, pixel dimensions and format: 200KB is lean for a 4000x3000 JPEG but heavy for an 800x600 one. PNG is allowed the most bits per pixel because it is lossless, then lossless WebP, JPEG, lossy WebP and AVIF. The tool does not look at what the image shows, so it cannot tell a photo from an infographic saved in the same format and size.

Should I rate images before or after upload to CMS?

Both. Before upload to verify the source asset is acceptable; after upload via the CMS-served URL to confirm your CMS isn't adding weight through re-encoding, watermarks, or wasteful resizing. The tool asks for the image with a browser-style Accept header, so a CDN that picks WebP or AVIF from that header serves the file a browser would get.

What happens to images I upload?

Processed in-memory and discarded. We do not retain the file, do not log content, and do not associate the rating with the image after the request returns.

Free Image Compression Rating Tool

Get an A-F grade and 0-100 score for a JPEG, PNG, WebP or AVIF image, based on its weight per pixel. Image URL or upload up to 15 MB, one-line verdict. Free, no signup.

4.6on G2

4.7on Trustpilot

How to use the Image Compression Rating Tool, step by step

Real screenshots of the tool, taken while running it.

1
Paste an image address
Paste the address of the image file itself, or switch to Upload Image to rate a file from your computer.
2
An image URL in place
Use the address of the image, not the page it sits on: right-click the image and copy its address.
3
Read the grade
You get a letter rating, a score out of 100 and a one-line verdict. The grade measures file weight per pixel for the format, not how the image looks.

What the Compression Rating Tool does

Images are often the heaviest files on a page. The Compression Rating Tool gives you a quick A-F grade for any JPEG, PNG, WebP or AVIF image, the fast way to spot which assets need to be compressed before they hurt Core Web Vitals.

Paste an image URL or upload a file. The tool divides the file size by the pixel count (bits per pixel) and compares it with thresholds for JPEG, PNG, WebP or AVIF. A means well-optimized; F means the file is heavily oversized for its dimensions and format. Re-export, re-rate, ship.

How to rate an image

Five steps from image to optimized.

Pick URL or upload

Paste an image URL or upload a file directly.

Click Rate Image

The tool reads the image, divides its file size by its pixel count, and grades the result against thresholds for its format.

Read the verdict

See your A-F letter grade, 0-100 score, and a one-line verdict explaining the result.

Compress if needed

For C/D/F, run through the Image Compressor or re-export from your design tool.

Re-rate to verify

After compression, rate the new file. Aim for A or B.

When developers and SEOs use it

Six common workflows.

Pre-publish image QA

Rate every hero image before pushing a blog post live. Anything below B gets compressed first, so heavy images are caught before they slow the page.

Performance audit sprint

You inherited a slow site. Run hero images through the rater; the F-rated ones are the quickest wins.

CMS upload validation

Some CMSes silently re-encode images at upload. Rate the served URL after upload to verify nothing got worse.

Designer handoff QA

Confirm that exported assets from Figma or Photoshop meet web-readiness standards before they hit your CMS.

Newsletter image checks

Images in an email download when the reader opens it. Rate header and product images before sending so a heavy file does not slow the email down.

E-commerce product photo audit

Run every category page hero through the rater and compress the D and F images first. Lighter images mean faster category pages.

Platform-specific setup guides

How to deploy compression on the platforms most teams ship from.

WordPress

Install ShortPixel or Smush; rate before and after to verify the plugin is doing its job.
For new uploads, turn on WebP or AVIF output in your image optimization plugin if it offers one.
For old images, run the bulk optimizer; rate a sample of pages after to confirm.

Webflow

Convert JPEG and PNG assets to WebP or AVIF with the image conversion tool in the Assets panel.
The conversion replaces the original file, so download a backup first.
Rate the served URL afterwards to confirm the smaller file is live.

Shopify

Shopify resizes images on its CDN with {{ image | image_url: width: 800 }}. Request the size your template displays, not the original.
For lookbook and editorial assets, manually compress with WebP.
Rate served versions to confirm theme isn't serving the original at full size.

Next.js / React

Use next/image with the right priority and sizes attributes for srcset generation.
For external CDN images, configure remotePatterns and let Next.js optimize.
Verify with this rater after deploy.

Static site generators

Hugo and Astro have built-in image processing; Jekyll needs a plugin such as jekyll_picture_tag.
Configure auto-WebP and responsive srcset.
Spot-check post-build by rating a sample of generated images.

Common errors and how to fix them

Eight issues teams hit when optimizing image assets.

URL fetch fails

Cause: The server hosting the image blocks automated downloads or needs a login, or the URL points to a web page rather than the image file.

Fix: Copy the image address itself, or save the image and use the Upload tab.

Low score on a small image

Cause: Format is wrong (PNG for photo), the quality setting is too high, or the file carries large metadata.

Fix: Re-export as WebP at quality 85 or JPEG at quality 80.

High score but page still slow

Cause: Multiple medium-rated images on the same page compound.

Fix: Audit every image on the page. Total page weight matters, not individual scores.

Same URL rates differently later

Cause: The server returned a different file: a new upload, a CDN re-encode, or another format variant. The grade itself is deterministic, so the same file always gets the same score.

Fix: Save the file and upload it to rate exactly that file.

PNG photo rated D or F

Cause: PNG is lossless: bad for photos. Better for icons and screenshots.

Fix: Convert to JPEG or WebP for photos.

WebP image rated lower than expected

Cause: Lossy WebP is held to a tighter threshold than JPEG (lossless WebP has its own, looser one), and a WebP saved at quality 100, or saved lossless when the image is a photo, is much larger than it needs to be.

Fix: Re-export as lossy WebP at quality 85 and compare the two side by side.

Score is high but file is huge

Cause: Image dimensions are very large; the algorithm rates relative to dimensions.

Fix: Resize to actual display dimensions before serving.

Large image is rejected

Cause: The limit is 15 MB per image, and a download from an image URL fails if the server stops responding for 12 seconds.

Fix: Resize it to the size it is displayed at, then rate the smaller file.

The thresholds behind the grade

The most bits per pixel each format can carry and still score 80, a B. The JPEG, WebP and AVIF lines are the sizes Lighthouse's image audits (version 12) expect of a well-compressed image; the PNG line sits near the median PNG on the web, 3.8 bits per pixel in the HTTP Archive's 2024 Web Almanac. Lossless WebP gets 3.0, because Google's WebP documentation puts lossless WebP 26% below PNG. A needs three quarters of the line or less, the score falls to 70 (C) at 1.5 times the line and 60 (D) at twice it, and it reaches 0 at six times it.

2.0

JPEG: most bits per pixel that still earns a B

1.6

Lossy WebP: most bits per pixel that still earns a B

1.33

AVIF: most bits per pixel that still earns a B

4.0

PNG: most bits per pixel that still earns a B

Frequently asked questions

Twelve answers covering image compression rating.

Related free tools

Other utilities that pair with the Compression Rating Tool.

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Image URL or upload, A-F grade, one-line verdict. Free, unlimited, no signup.

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