Converting a lossy format like JPEG into a lossless format like PNG can make the file bigger, not smaller. That's because a lossless format must store every pixel exactly as it now exists — including the blocky or blurry compression artifacts JPEG already introduced — with no further compression shortcuts available.
For example, consider a typical case: a 200KB JPEG photo, when converted to PNG, can easily balloon to 800KB or more. PNG's lossless compression can't exploit the smooth gradients JPEG normally handles efficiently, so every one of JPEG's small compression artifacts becomes "real" pixel data that PNG must faithfully preserve.
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Compare formats and shrink your image with our free converterThe general principle: lossy vs. lossless
Lossy formats — JPEG, WebP, and AVIF at typical quality settings — throw away image data you can't get back, in exchange for much smaller files. The human eye rarely notices what's missing, so the size savings are essentially free.
Lossless formats — PNG, BMP, and GIF's color-limited compression — keep every pixel exact. That's valuable for text, line art, and screenshots, but it usually produces larger files for photographic content, especially content that was already lossy-compressed once before.
Rule of thumb for file size after converting
- Lossy → lossless (e.g., JPEG → PNG) usually increases file size.
- Lossless → lossy (e.g., PNG → JPEG) usually decreases file size significantly.
- Lossy → lossy (e.g., JPEG → WebP) usually decreases file size modestly.
- Re-compressing the same lossy format repeatedly (JPEG → JPEG → JPEG) degrades quality further each time without necessarily shrinking size much after the first pass.
Convert to a lossy format like JPEG, WebP, or AVIF instead of PNG. See our guide to reducing image size without losing quality for the settings that actually work.
Frequently asked questions
Why is my PNG bigger than my original JPEG?
PNG is a lossless format, so it must store every pixel exactly as it exists in the source image, including the compression artifacts JPEG already introduced. Because it can't discard any data the way JPEG does, PNG often produces a larger file than the original JPEG, especially for photographic content.
How do I actually make an image smaller?
Convert to a lossy format such as JPEG, WebP, or AVIF and use a quality slider around 75-90%. Our reduce image size guide walks through exactly how to do this without a visible quality hit.
Does this mean PNG is a bad format?
No. PNG is ideal for screenshots, text, line art, and anything needing exact pixels or transparency. It's just the wrong tool for shrinking photographic content.