Why Is My JPG Bigger Than My PNG? (Tested on Screenshots and Photos)

Why does JPG make screenshots, charts and logos bigger than PNG?

PNG uses lossless compression based on the Deflate algorithm, as defined in the W3C PNG specification. When an image has large flat areas, repeated pixel patterns, or straight horizontal lines, PNG packs them compactly without discarding a single pixel.

JPG was built for continuous-tone photographs. It divides an image into 8x8 pixel blocks and applies a Discrete Cosine Transform. Human vision does not notice tiny variations in smooth gradients, so JPG discards high-frequency details to save storage space.

Screenshots, logos, and charts are the opposite of photos. They contain crisp text, sharp contrast borders, and solid backgrounds. When an 8x8 block contains black text on a white background, the JPG encoder detects an extreme high-frequency boundary. To encode that sharp edge, JPG must spend many bytes, yet still introduces ringing artifacts and blur. You get a larger file that looks worse.

Why do photos get much smaller in JPG while graphics grow?

Continuous-tone photos behave differently from computer graphics. A camera photo contains millions of subtle color shifts and sensor noise. Every pixel differs slightly from its neighbor.

PNG cannot compress photographic noise well. Because it is lossless, it must record every microscopic color change, producing huge files.

In our benchmark tests, a 1600x1067 colourful synthetic pattern with photo-like fine detail was 4,282.8 KB as a PNG. Converted to JPG at Balanced 85 in Chromium, it dropped to 188.8 KB: about 23 times smaller. JPG threw away fine detail that PNG had to keep.

For photographic images, JPG is much smaller. For flat shapes, text, and screenshots, the opposite happens.

Why does JPG Quality 100 multiply your file size?

Setting the quality slider to 100 does not mean "same as original" or lossless. That is a common misunderstanding.

At quality 100 the encoder uses the smallest rounding steps it has, so it keeps almost every detail, including noise around edges. It is still lossy, but the file gets much bigger.

On a clean screenshot, file size explodes. In our tests, an article screenshot of 122.8 KB grew to 496.8 KB at Max 100 in Chromium: four times larger than the PNG.

When an output JPG is larger than the input PNG, our tool warns you:

"123 KB → 497 KB (304% larger — try a lower quality)"

The tool offers four presets: Small 70, Balanced 85 (default), High 92, and Max 100. Balanced 85 works well for photos, but for screenshots, even 85 can exceed the PNG size.

How we tested file sizes across Chromium and Firefox

To understand exactly when and why JPG becomes larger than PNG, we ran controlled measurements on 23 October 2026.

Every test PNG was drawn onto a clean white canvas element and exported using the standard browser method canvas.toBlob(..., "image/jpeg", q). This matches the exact client-side conversion logic implemented by our browser tool. Tests were automated using Playwright in Chromium and Firefox. All reported sizes are in kilobytes, where 1 KB equals 1024 bytes.

We selected six test files representing common real-world use cases:

1. A 1366x768 screenshot of a guide article page with headings and paragraphs.
2. A 1366x768 screenshot of the site home page with cards and buttons.
3. A 1200x630 flat share graphic with solid brand colors and large typography.
4. An 800x450 bar chart containing colored bars, axis lines, and numeric labels.
5. A 600x200 computer-drawn signature line on a white background.
6. A 1600x1067 colourful synthetic pattern with photo-like fine detail (this is a synthetic benchmark pattern, not a real camera photo).

Here are the measured file sizes in Chromium (Chrome, Edge, and Android Chrome):

We repeated the exact same test sequence in Mozilla Firefox:

The test data highlights five clear observations:

• For screenshots, graphics, and charts, the Balanced 85 setting creates JPGs that are either slightly larger or roughly equal to the original PNG. At High 92 and Max 100, the JPG is significantly larger. The article screenshot is four times larger at quality 100.
• The bar chart was larger as a JPG at settings 85, 92, and 100 in Chromium, and larger at every single setting in Firefox.
• The photo-like pattern experienced massive reductions in both browsers, falling from 4,283 KB down to 189 KB at Balanced 85 in Chromium.
• Different browsers use different underlying JPEG encoders. Firefox produced larger output files than Chromium across all test conditions at the same nominal quality setting. At quality 92, the article screenshot was 268.2 KB in Firefox compared to 162.3 KB in Chromium.
• Small 70 was the only quality preset in Chromium where every screenshot came out smaller than its corresponding PNG.

What should you do if your JPG is too big?

If your converted JPG is larger than your PNG, choose your next step based on where the file will be used:

• Keep the PNG if you have a choice. For web publishing or document embedding, keep the original PNG. The MDN guide to image formats puts it plainly: "For screenshots, diagrams, logos, and line art, prefer lossless encoding."
• Use Small 70 when a portal requires JPG. Some exam and recruitment portals accept only JPG. If you must submit a screenshot or signature in JPG, set the slider to Small 70 and check the result line.
• Use target compression for strict kilobyte limits. When a portal requires a file under 50 KB or 20 KB, guessing slider numbers is slow. Use Compress Image with the "Target size" option to hit an exact kilobyte threshold.
• Switch to WebP for modern websites. If your website accepts modern formats, WebP keeps transparency and is usually smaller than PNG. You can convert files using the Image Converter.

When not to convert PNG to JPG

Sometimes keeping the PNG is the right choice:

• You need transparency. JPG cannot store transparency; see-through areas are filled with a solid background.
• The image has sharp text or fine lines. JPG adds blur around letters, making text harder to read.
• You want the smallest file for the web. For modern browsers, WebP often beats both formats. Our image format test for website speed compares JPG, PNG, WebP and AVIF.

Our tool has clear boundaries:

• Accepts PNG input only.
• Up to 10 images at once, 25 MB each.
• Cannot compress to a fixed KB limit on its own; that requires Compress Image.

FAQ

Why did my screenshot get bigger after converting to JPG?

Screenshots contain flat colors and sharp text. PNG compresses these patterns compactly without data loss. JPG splits the image into 8x8 blocks and spends extra bytes trying to encode sharp contrast borders, inflating file size.

Does JPG quality 100 make the image lossless?

No. JPG is always lossy. Quality 100 only throws away less, which is why the file grows so much without looking clearly better.

Why does Firefox produce larger JPGs than Chrome at the same quality?

Each browser has its own JPEG encoder. One clear difference we measured: from quality 90, Firefox stores colour at full resolution, while Chromium keeps colour at quarter resolution until 100. Full colour costs more bytes, so the same screenshot at 92 was 268.2 KB in Firefox and 162.3 KB in Chromium.

Can the PNG to JPG tool hit an exact KB size for online forms?

No. The tool provides quality presets from 70 to 100, but cannot target a specific byte count. To hit an exact limit like 20 KB or 50 KB, use Compress Image with Target size.

Choose the right format and settings

JPG is designed for photos; PNG is built for screenshots, charts, and graphics. If you need a JPG for an exam or portal, use quality 70 or 85 rather than 100. When you are ready to convert, turn your PNG into a JPG on QuickFileTools. All processing happens in your browser, so your files stay on your device.

Related guides: JPG quality 70 vs 85 vs 92 vs 100 · PNG to JPG under 50 KB for online forms · Why your PNG turns black when converted to JPG · Photo and signature size for online forms