WebP vs PNG: The Honest Comparison

Every comparison article says "WebP is better for the web, PNG is better for editing." That's basically true, but it glosses over the situations where the answer is less obvious. I've been running an image converter for over a year, and I've tested this combination more than I ever expected to. Here's what I actually found.

The core technical difference

PNG is lossless. Every pixel in the file is stored exactly as it was in the original. When you open a PNG, you get a perfect copy. When you save a PNG, nothing is discarded. That's why PNG files tend to be large for photographs — photographs have millions of slightly different colored pixels, and storing all of them precisely costs space.

WebP can work in both lossless and lossy mode. Lossy WebP — which is what most converters default to — discards some data that's unlikely to be noticed. The algorithm is designed to prioritize what the human eye pays attention to (sharp edges, high-contrast areas) and sacrifice what it doesn't (fine random texture in smooth areas). The result is a much smaller file that usually looks identical to the original.

There's also lossless WebP, which keeps everything but still compresses more efficiently than PNG in most cases. That's worth knowing because "WebP vs PNG" isn't a single comparison — it's actually at least three different comparisons depending on which WebP mode you're using.

When WebP clearly wins

For web delivery of photographs, WebP is the obvious choice. It'll be meaningfully smaller than an equivalent JPG (typically 25–35%) and dramatically smaller than a PNG of the same photo. If your priority is page load speed, there's really no argument for serving a photo as PNG.

Product images on e-commerce sites are a perfect WebP use case. Clean backgrounds, defined edges, consistent lighting — WebP compresses these efficiently. I've seen product image libraries reduce by 40–50% in total size after a WebP conversion, with no complaints about visual quality.

Blog images, hero images, background images — anything photographic that's being served on a webpage. WebP.

When PNG is actually the better choice

Here's the part most comparison articles skip: PNG sometimes wins on file size too, not just on quality.

Screenshots are the clearest example. A screenshot of a code editor or a UI has large areas of flat color, sharp text, and very consistent pixel values in blocks. PNG compresses those extremely efficiently. I've converted screenshots to WebP expecting smaller files and ended up with larger ones. If you're writing technical documentation or tutorial content with lots of screenshots, test both before assuming WebP is smaller.

The same applies to simple graphics, diagrams, and anything generated by software rather than a camera. Computer-generated images with flat fills and sharp edges are PNG's natural habitat. WebP's compression algorithm is optimized for photographic content and can actually perform worse on these.

PNG also wins when your images will be downloaded and edited by someone else. WebP support in desktop editing software is still patchy — older Photoshop versions, some Windows apps, Preview on older Macs. If you're sending deliverables to clients or sharing files through a design workflow, PNG is more universally compatible.

The transparency question

Both formats support transparency, so this is often cited as a reason to use PNG over JPG specifically — not over WebP. If you need transparent backgrounds, both WebP and PNG can handle it. WebP typically produces smaller files with transparency too, so for web delivery of transparent graphics (like logos on various backgrounds), WebP is generally the better choice.

The one caveat: if the transparent asset will be opened in design software or shared for editing, PNG is safer for compatibility reasons.

What this means for page speed and SEO

Images are often the largest contributor to page weight, and page weight directly affects how fast your site loads. For most websites with photographic content, switching from PNG (or even JPG) to WebP is one of the fastest wins available.

But I want to push back on the framing that this is primarily an "SEO strategy." It's a user experience improvement that happens to have SEO benefits. Your visitors notice a slow site. Google's Core Web Vitals measurements reflect real user experience. The reason to optimize images is that it makes your site more pleasant to use — the rankings benefit follows from that.

If you want to know whether images are your actual bottleneck, run your URL through PageSpeed Insights. It'll tell you specifically whether image size is contributing to a slow LCP score. If it's not flagging images, optimizing them won't move the needle much.

My actual recommendation

Default to WebP for anything photographic going on a website. Use PNG for screenshots, computer-generated graphics, and anything people will download and edit. When in doubt, convert both and compare file sizes — it takes 30 seconds and the answer will be definitive for your specific image.

One thing I'd add: stop keeping PNG as your only copy of something. I see this constantly — someone has a PNG that was originally a JPG, and they've lost the original. Keep your source files. Export to whatever format makes sense for each destination. Format choice should be per-output, not per-asset.