JPG to WebP: a checklist before you convert

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Converting a JPG to WebP is a one-click job, but it is easy to end up with a file that is bigger, softer or unusable where you wanted to put it. Work through this checklist first, then the short steps, then the measured example that shows why the order matters.

Check 1: do you actually need WebP?

The reason to convert is almost always a lighter file on a web page. MDN says lossy WebP images are on average 25 to 35% smaller than JPEG images of visually similar compression levels, and Google's FAQ gives about 30% more compression than JPEG on average. Those are published averages from their own tests. If the picture is for email, print or a form that lists JPG, there is little to gain and some risk. See WebP vs JPEG for the comparison.

Check 2: can everything that will open it handle WebP?

MDN describes WebP as broadly supported in the latest versions of major browsers, but without deep historical support, and recommends a JPEG or PNG fallback. It adds a specific caution for Safari on macOS: support depends on both the Safari version and the macOS version, with Safari 14 and macOS Big Sur (11) or later required. Google's FAQ lists Safari 14 and later as supporting WebP too.

Browsers are only part of it. Editors, print shops, marketplaces and email programs are separate cases and I did not find an authoritative support table for them, so check the destination's own instructions. If you are unsure, keep the JPG alongside.

Check 3: is this a photograph?

JPG to WebP suits photographs, where lossy compression works well. If your JPG is a screenshot or a logo, it already carries compression noise around its edges, and a second lossy save compounds it. MDN recommends lossless encoding for sharp content such as diagrams and line art.

Check 4: do you have the original?

A WebP made from a JPG is a second lossy generation. Detail the JPG dropped is gone for good, and the WebP adds its own approximations on top. If you still have the camera original or a lossless master, convert that, not the JPG. If you do not, keep the JPG as your best surviving copy and treat the WebP as disposable.

Check 5: can the file get bigger?

Yes, and Google says so itself. Its FAQ states that converting a JPEG saved at quality 80 to a WebP at quality 95 will usually give a larger file, because the source quality is often unknown. It suggests lowering the target quality if files keep growing. Our tool does not offer a quality slider; it asks the browser for 0.92 and does not tell you what quality your JPG used. That makes the comparison step below important.

The steps

1. Open JPG to WebP and add one image (up to 50 MB and 40 megapixels).
2. Convert. It runs in your browser and the file contents are not uploaded to ConvertMango's conversion service.
3. Your browser must be able to export WebP. MDN's page on the canvas export method says browsers must support PNG while many also support others including WebP, and that a format the browser cannot produce is exported as PNG. If the download is a PNG, switch to a current mainstream browser.
4. Compare the new file with the JPG: size first, then zoom in on faces, skies and edges.
5. Use the WebP only if it is clearly smaller and looks the same to you. Otherwise delete it.

A measured example

I took a CC0 photograph at 1600 x 1063 pixels and saved it as a JPG at Pillow quality 92. That JPG weighed about 302 KB. I then re-encoded the JPG as lossy WebP with Pillow 11.3.0 and libwebp 1.5.0 at three settings, and once as lossless.

This is an illustration with one image and Pillow's encoder, not a benchmark, and browsers will give different sizes. Two things are worth noticing. At matching quality 92 the WebP was about a quarter smaller, close to the published 25 to 35% range. And the lossless row is the trap: asking for a lossless WebP from a JPG gave a file more than three times the size of the JPG, which agrees with Google's note that converting a JPEG to lossless WebP or PNG can produce a larger file. Lossless does not mean better when the source was already lossy.

I did not compare how the pictures look, so the table says nothing about visual quality at the lower settings.

Check 6: transparency does not come into it

A JPG has no transparency, so the WebP from a JPG will have none either. If you want a see-through background, you need the image cut out in an editor or another source first. If you start from a PNG instead, PNG to WebP keeps transparency.

What to do next

If the WebP is a keeper, serve it with a JPG fallback and keep the JPG on your drive. If a recipient cannot open it, WebP to JPG takes you back, though not to a better JPG than you started with. For the format basics, read what is WebP and what is JPEG, and for broader size comparisons see the image format file size table.

Convert it now: JPG to WebP.

Frequently asked questions

Related tools

More guides

Sources

Plain-text references. Facts that could not be checked against a primary source were left out.

1. Google, 'WebP Frequently Asked Questions', https://developers.google.com/speed/webp/faq
2. MDN Web Docs, 'Image file type and format guide', https://developer.mozilla.org/en-US/docs/Web/Media/Guides/Formats/Image_types
3. MDN Web Docs, 'HTMLCanvasElement: toBlob() method', https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toBlob