Is the file growing the converter's fault?

No, this is an expected result that follows from the nature of the formats. When WEBP works in lossy mode, it shrinks the file by permanently discarding detail the eye struggles to notice. PNG discards no pixel information at all; it only packs repeating patterns losslessly. These are two different approaches designed for two different goals, and the size difference is the direct consequence.

Is the larger PNG file higher quality?

It is not visually higher quality; it looks identical to its source. The extra data PNG stores is not new detail but a less efficiently packed version of the same picture. If the source WEBP was compressed lossily, the banding and halos in it sit unchanged in the PNG as well. PNG's real gain is not in appearance but in the fact that no new loss occurs each time you save the file from here on.

Is there a way to reduce the size increase?

Bringing the image's resolution down to the size you actually need is the most effective method; PNG size is directly proportional to pixel count. In addition, on graphics with a limited color palette some tools can achieve a marked reduction by lowering the color count, though this creates visible degradation on photographs. The real question should be this: does this image genuinely need to be a PNG, or was it chosen out of habit?

How much growth counts as normal?

It would be wrong to give a single ratio, because the result depends entirely on the image's content. On photographic content — images where every pixel differs from its neighbor — the increase is very pronounced. On logos, icons and screenshots carrying large flat color areas, the increase stays far more limited, sometimes almost nonexistent. Setting an expectation without looking at the content is misleading.

Why Does the File Get Bigger When You Convert WEBP to PNG?

You ran into a result you did not expect

You converted a WEBP file of a few hundred kilobytes to PNG and the output is measured in megabytes. The first reaction is usually "the converter is broken." It is not. This is an entirely predictable result once you know how the two formats work.

In this article we explain the technical reason for the growth and, more importantly, clarify when that growth is an acceptable price and when you should question the conversion itself.

Two different compression philosophies

WEBP discards information in lossy mode. This format, designed by Google for the web, identifies the detail the human eye struggles to notice and permanently deletes it. Slight color fluctuations in a sky, fine tonal differences within a shadow, high-frequency texture detail — some of these get discarded. The remaining data takes up far less space. WEBP also offers a lossless mode, but most of the WEBP files you will encounter on the web are in lossy mode.

PNG discards nothing. PNG's compression is entirely lossless. All it does is find repeating patterns in the image and pack them with a more efficient representation. If there are a thousand identical white pixels side by side, for instance, it can store that as a short expression meaning "a thousand whites." When you open the file, those thousand pixels come back in full.

That is exactly where the difference emerges: WEBP shrinks by reducing data, while PNG only packs more cleverly while preserving data. If there is little repetition to pack, there is not much PNG can do.

Why does it grow so much on photographs in particular

Picture a landscape photo. The sky is not a single blue; every pixel is a slightly different shade from its neighbor. A grassy field consists of hundreds of different shades of green. In a portrait, the skin surface carries constant micro-variations.

In content like this, there is almost no repeating pattern for PNG to look for. The compression algorithm scans through, finds nothing to pack, and is forced to store most of the pixels in something close to their raw state. The result: a large file.

On the same photograph, WEBP works in lossy mode, discards some of those micro-differences as "invisible to the eye" and produces a far smaller file. Visually the difference is almost nothing, but the amount of data is entirely different.

Why growth stays limited on logos and screenshots

Now picture a logo: a few flat colors, sharp edges, large single-color areas. Or a screenshot: a flat background, flat-colored buttons, text.

On this content PNG works very efficiently. It packs large single-color areas into extremely short expressions. The size increase either stays very limited or does not happen at all. That is why PNG is a natural and correct choice for content like logos, icons, screenshots and diagrams; this is exactly the job the format was designed for.

What you get in return for the growth

The increase is not for nothing. When you move to PNG, you gain three concrete things.

New losses stop. No matter how many times you save the file from here on, quality stays constant. Had you been working in a lossy format, every save would have added new artifacts on top of the previous ones. If you will be editing through multiple stages, this is a decisive advantage.

Transparency is preserved. WEBP's alpha channel transfers to PNG in full. Soft edges, semi-transparent shadows and fully transparent regions stay exactly as they were.

Compatibility widens. Finding a program that does not recognize PNG is nearly impossible. Programs that do not recognize WEBP, on the other hand, are still plentiful — older image editors, corporate document systems, prepress tools.

When you should reconsider the conversion

Let us be honest here: in some situations, moving to PNG is an unnecessary cost.

If the image is a photograph and transparency is not required. Converting a landscape or a product shot to PNG multiplies the file size several times over and delivers no visible gain whatsoever. If you need to convert for compatibility, JPG is a far more suitable target.

If you will publish on the web. WEBP was designed for exactly this and every modern browser supports it. Converting to PNG increases page weight and gives visitors nothing.

If the file already opens everywhere you use it. The purpose of a conversion should be to solve a problem. If there is no problem, there is no need for a solution.

If transparency has to be preserved or you will be editing through multiple stages, converting WEBP to PNG is the right decision and the size increase is the reasonable price of those gains.

In summary

The file growing when you move from WEBP to PNG is not a malfunction but the direct consequence of the difference in the two formats' design philosophies. WEBP shrinks by discarding information; PNG preserves information and merely packs it efficiently. Because there is little repetition to pack in photographic content, the increase is pronounced; on content with lots of flat color areas, such as logos and screenshots, it stays limited. You pay that price in exchange for preserving transparency, stopping new losses and gaining compatibility. If you do not need those three things, question the conversion itself.