How to Compress a WebP Image
A WebP can still be heavy. How to shrink one without leaving the format, what happens to transparency, and when a smaller file means fewer pixels.
To compress a WebP image, open Compress WebP, drop in the file, move the Compression quality slider below its 0.75 starting point or type a limit into the target size box, then click Compress and download. The file stays a WebP, transparent areas stay transparent, and the work happens in your browser, so the image is never uploaded.
WebP is already a compact format, which is why a heavy one is surprising. The cause decides the fix, so it is worth a minute before you reach for the slider.
Why is my WebP file still so big?
A WebP is usually heavy for one of three reasons:
- It was saved at a high quality setting. The top of a quality scale tends to cost the most bytes for the least visible gain, and this is the case compression fixes best.
- It has more pixels than it will ever be shown at. A photo several thousand pixels wide, displayed in a column a few hundred pixels wide, carries detail nobody sees. Resizing fixes that better than compressing does (see below).
- It was saved as lossless WebP. Lossless mode keeps every pixel exactly, which suits logos and screenshots but makes a photo much heavier than a lossy save of the same image.
For the wider picture, why an image file gets so big covers the same causes across every format.
How to compress a WebP image, step by step
- Open Compress WebP and drop your file on the page, or pick it with the file browser. The tool takes WebP files only: a JPG is refused with a message that it "isn't a supported image type". For those, use Compress JPG or Compress PNG.
- Read the estimate under the controls. Once the file loads, an "Estimated output" line shows the new size and the percentage saved, and it updates a moment after you change a setting.
- Drag Compression quality down. It runs from 0.3 to 1 in steps of 0.05 and starts at 0.75. Go lower only if the estimate is still too big.
- If a website or form gives you a hard limit, type it into "Target max size in MB" instead. The next section explains how that box behaves.
- Click Compress, then download. A single file keeps its original name; several files come as one zip, and the estimate line covers only the first of them.
Quality slider or target size: which should you use?
Use the slider when you care how the image looks, and the target box when someone else has set a number. They work differently, and only one of them can change the image's dimensions.
| Compression quality | Target max size in MB | |
|---|---|---|
| What it changes | Encoder quality only | Quality first, then width and height if needed |
| Dimensions | Never change | Can come back smaller |
| When it can't help | Returns your original file | Returns the smallest file it managed |
| Best for | Images on your own site | Upload limits and asset budgets |
When the target box has a number in it, the slider is ignored. If your file is already under the target, you get it back untouched. Otherwise the tool searches for the highest quality between 0.40 and 0.92 that fits, and if even 0.40 is too big, it shrinks the image and tries again, for up to eight passes in all. In our test, a detailed 1600 x 1000 WebP given a 0.1 MB target came back at 883 x 552.
One catch with small limits: the box counts 1 MB as 1,048,576 bytes, so 0.1 means 104,858 bytes, which is over a 100 KB limit whichever way the form counts a kilobyte. Type 0.09 (about 94,000 bytes) to stay under it. For the KB-sized limits common on forms, compressing an image under 100KB walks through the dedicated tools.
What happens to transparency, animation and quality?
Transparency survives. In our test, a WebP with a transparent corner came back with that corner still fully transparent, at every setting.
Animation does not. The tool redraws the image on a canvas, which holds a single frame, so a compressed animated WebP comes back as one still picture. If the tool hands back your original instead, because it was already under the target or the re-encode was not smaller, the animation is intact but nothing was compressed. This tool is for static WebP images.
Quality loss adds up. Every setting below 1 is a lossy re-encode, so compressing a WebP that was already compressed throws away detail a second time. That is generation loss, and the way around it is to start from the original JPG or PNG if you still have it. Converting an image to WebP covers that route. A lossless WebP put through the tool below 1 comes out as a lossy WebP. At 1, if the re-encode isn't smaller than your file, the tool hands back your original unchanged.
When compressing isn't the right fix
If the image simply has too many pixels, resize it first. Resize Image keeps a WebP as a WebP, transparency included, and fewer pixels means a smaller file at any quality setting. Compress afterwards if it is still heavy.
If the site you're uploading to won't take WebP at all, a smaller WebP won't help. WebP to JPG converts it, and fills any transparent areas with white because JPG has no transparency. For images on your own pages, optimizing images for a website puts resizing, format and compression in order.
FAQ
Why did my WebP come back the same size?
At a quality setting, the tool never returns a file bigger than the one you gave it. If the re-encode isn't smaller, you get your original back. With a target size, a file already under the target is also returned as it is. Lower the slider or the target and try again.
Will compressing a WebP change its dimensions?
Not with the quality slider. With a target size, it can: if the lowest quality the tool tries is still too big, it scales the image down and tries again, for up to eight passes.
Can I compress several WebP files at once?
Yes. Drop them in together and they are compressed with the same settings, then downloaded as one zip. The size estimate before you click only covers the first file.
Is my WebP uploaded anywhere?
No. The compression runs in your browser on your own device, so the file never leaves it.