PNG vs JPEG File Size: Why the Gap Is So Large

It's a common surprise: save the same photo as both PNG and JPEG, and the PNG version can easily be five to ten times larger, sometimes more. This isn't a bug or an inefficiency in PNG — it's a direct consequence of the fundamentally different jobs the two formats are built to do.

The core reason: lossless vs lossy

PNG uses lossless compression, meaning it has to preserve every single pixel's exact original value with no exceptions. JPEG uses lossy compression, deliberately discarding image information that's judged least noticeable, which allows it to achieve far smaller file sizes at the cost of no longer being a perfect, bit-for-bit copy of the original. For photographic content specifically, this trade-off heavily favors JPEG, since photos rarely need pixel-perfect exactness and have plenty of the kind of visual redundancy lossy compression exploits well.

Why the gap is especially large for photos

Photographs are full of subtle, continuous color gradients and fine texture — exactly the kind of content lossless compression struggles to shrink efficiently, since there's comparatively little exact repetition for it to exploit, while lossy compression's perceptual model handles this kind of content very efficiently. This is why the PNG-vs-JPEG size gap is usually most dramatic on photographs specifically, and considerably smaller (sometimes even reversed) on simple graphics like logos or screenshots with large flat color areas.

When PNG's larger size is worth it

For content where every pixel needs to stay exactly accurate — a logo with crisp edges, a screenshot containing readable text, a diagram with fine lines — PNG's lossless guarantee is genuinely worth the larger file size, since JPEG's lossy compression tends to introduce visible artifacts specifically around sharp edges and text, the exact content types PNG handles best. PNG is also the standard choice whenever an image needs transparency, which JPEG doesn't support at all.

When it isn't worth it

For ordinary photographs destined for a website, an email, or social media, PNG's lossless exactness rarely provides a visible benefit over a well-compressed JPEG or WebP, while costing significantly more in file size and load time. Reserving PNG specifically for graphics, screenshots, and transparency needs — and using JPEG or WebP for photographic content — is the standard, practical rule most professionals follow rather than defaulting to one format for everything.

A quick way to check which format actually wins for a specific image

When genuinely unsure which format will produce the smaller file for a particular image, the most reliable approach is simply exporting both and comparing — most image editing tools show file size during export, making a direct side-by-side comparison quick to check. This is especially worth doing for borderline content, like a simple illustration with only a few flat colors, which sometimes compresses smaller as PNG than as JPEG, defying the usual photo-favors-JPEG, graphic-favors-PNG rule of thumb.