WebP: What It Actually Is, Why It Works, and Where It Falls Short

WebP is the format I recommend most often when someone asks me which image format to use for their website. But "just use WebP" isn't a complete answer. There are situations where WebP isn't the right call, and the reasons why WebP works are worth understanding — because they affect how you use it.

How WebP compression actually works

Google developed WebP in 2010, basing it on the same technology used in VP8 video encoding. Most people use WebP without knowing any of this, and that's fine — but understanding the core idea helps explain why it beats JPG in some situations and not others.

JPG compresses images by dividing them into 8×8 pixel blocks and roughly approximating the color values in each block. It works well for photographs because our eyes tolerate small color errors in complex scenes. But at block boundaries — sharp edges, text, anything with a hard transition — you can see the seams. Those blocky artifacts at high compression are JPG's signature flaw.

WebP uses a different approach called predictive coding. Instead of treating each block independently, it looks at neighboring blocks and tries to predict what the current block will look like, then only stores the difference between the prediction and reality. For images with smooth areas and gradients — like sky, skin, or backgrounds — the prediction is very accurate, so the "difference" is tiny, and tiny differences compress very well.

That's why WebP tends to do particularly well on product photos against clean backgrounds and travel photos with sky. The algorithm's predictions are good there. For images with lots of fine random texture — fabric, hair, grass — the predictions are less accurate and the advantage narrows.

WebP vs JPG vs PNG — what I actually measured

I'll save you the usual benchmark table with suspiciously round numbers. Here's what I found testing on 200 real images that people actually uploaded to this converter over the past few months:

The headline number you'll see cited everywhere — "WebP is 25–34% smaller than JPG" — is accurate as an average, but your actual results will vary quite a bit depending on the image content.

What WebP does and doesn't do for SEO

I want to be honest here because a lot of articles overstate this. WebP doesn't directly improve your search rankings. Google doesn't look at your image formats and give you points for using WebP.

What WebP does is make your images smaller. Smaller images load faster. Faster loading improves your Largest Contentful Paint (LCP) score, which is one of Google's Core Web Vitals. Core Web Vitals are a ranking signal. So the chain is: WebP → smaller files → faster LCP → better Core Web Vitals → potential ranking benefit.

In practice, if your site currently has a poor LCP score primarily because of large images, switching to WebP can make a meaningful difference. If your LCP is already good, or if slow images aren't your bottleneck, the SEO impact will be negligible. The tool that will actually tell you is PageSpeed Insights — run your URL there before deciding whether image optimization should be your priority.

Where WebP actually falls short

Three situations where I wouldn't default to WebP:

Files people will download and edit. Older versions of Photoshop, Preview on Mac, and the default Windows photo viewer have inconsistent WebP support. If you're sharing images with clients or colleagues who might open them in desktop software, JPG or PNG is safer.

Email. Most email clients don't support WebP. Images embedded in or attached to emails should stay as JPG or PNG.

When you need maximum encoding speed. WebP encoding is slower than JPG, especially at high quality settings. For workflows where you're processing large batches of images quickly, that can matter.

How to implement WebP properly

Browser support for WebP is now effectively universal for web browsing — I track it at around 97% of global users as of early 2026. The remaining 3% is mostly very old browsers and some corporate environments with locked-down configurations.

The safest approach is still to use the <picture> element with a fallback:

<picture>
  <source srcset="image.webp" type="image/webp">
  <img src="image.jpg" alt="Your image description" loading="lazy">
</picture>

One thing to be careful about: don't add loading="lazy" to your largest above-the-fold image (usually your hero image or banner). Lazy loading tells the browser to wait before fetching the image, which will actually hurt your LCP score. Use fetchpriority="high" on that one instead, and lazy load everything else.

Frequently asked questions