Images
Is WebP really smaller than JPG? A side-by-side test
We converted the same sample photos to JPG and WebP at the same quality setting and compared file sizes. Here are the numbers, and when WebP is worth it.
The short answer
In our test, yes: WebP files were about 20 % smaller than JPG files made from the same photos at the same quality setting, and WebP won for 8 of the 9 photos. But both formats are dramatically smaller than PNG for photos, and that difference matters far more than JPG versus WebP.
How we tested
We took 9 public sample photos from the scikit-image project, a mix of portraits, objects, a microscope image and an astronomy image, stored as PNG (6,072 KB in total). We converted all of them with JPG PNG WebP Converter in Chrome, once to JPG at quality 90 and once to WebP at quality 90, and added up the file sizes.
- PNG originals: 6,072 KB
- JPG, quality 90: 1,010 KB (83 % smaller than PNG)
- WebP, quality 90: 809 KB
One caveat: “quality 90” is not an identical setting across formats, because each encoder maps the number to its own internal settings. So treat the result as a fair everyday comparison rather than a lab measurement, and if you care about the last few percent, compare your own images side by side.
Why WebP tends to win
JPG dates from 1992 and compresses the picture in fixed 8×8 pixel blocks. WebP, released by Google in 2010, predicts each block from its neighbours and only stores the difference, which usually needs fewer bytes for the same detail. It also supports transparency, which JPG can’t do at all, so it can replace PNG for logos and cut-outs too.
When to stay with JPG
WebP is shown by all current browsers, so for a website it is a safe choice. Outside the browser things are less even:
- Many official forms, job portals and print shops accept only JPG or PNG.
- Some older photo editors and office software can’t open WebP.
- If someone else will download and reuse the picture, JPG is the format that opens everywhere.
A practical rule: WebP for images you publish on your own site, JPG for images you send to other people or upload to forms.
The bigger win: don’t use PNG for photos
The most striking number in this test is not WebP versus JPG. It is that converting photos away from PNG cut the size by 83 %. PNG is lossless, which is ideal for screenshots, diagrams and text, but it stores every pixel of a photo exactly and gains little from it.
If a photo is still too large after converting, reduce its pixel dimensions with Bulk Image Resizer or lower the quality in Compress Image.