Why converting a photo to PNG can make it bigger, not smaller — and a simple rule for picking the right format every time.
The three formats solve different problems, and picking the wrong one is the most common reason a "compressed" image comes out larger than the original. Here's the rule that actually holds up: match the format to what's in the image, not to what feels like the "best" format overall.
JPEG uses lossy compression tuned for photographic detail: gradients, natural light, texture. It throws away information a human eye barely notices and gets dramatically smaller files in exchange. At 80% quality, most photos are visually indistinguishable from the original while dropping to a fraction of the file size. This is the default choice for any photograph — product shots, headshots, backgrounds.
WebP is a newer format that generally produces smaller files than JPEG at the same visual quality, and it's supported by every modern browser. If you don't have a specific reason to need JPEG (like compatibility with an old system that only accepts .jpg), WebP is the better default for photos today.
PNG is lossless — it doesn't throw anything away, which is exactly why it's the right choice for screenshots, logos, and graphics with flat colors or sharp edges: nothing gets blurred or artifacted. But that same losslessness means PNG can't compress photographic noise and gradients the way JPEG or WebP can. Converting a photo to PNG often produces a file several times larger than the original — that's expected behavior, not a bug in whatever tool you're using. If a "compression" tool ever hands you back a bigger PNG from a photo, that's the lossless tradeoff working as designed, not a broken tool.
Photo → JPEG or WebP. Screenshot, logo, or flat-color graphic → PNG. If you're not sure which category an image falls into, ask whether it has smooth photographic gradients (JPEG/WebP) or sharp, flat-color edges like text and icons (PNG).