PNG to JPG

Transparent areas get filled with a solid white background, because JPG as a format simply does not support transparency. This is the biggest thing to know before converting. If your PNG has a transparent background, like a logo or icon, the result will have that logo sitting on a white rectangle. For most use cases this is totally fine, especially if you are uploading to a website or email where the background would be white anyway. But if you need to place the image over a colored background or another photo, you will want to keep it as PNG. In my experience, about half the people who convert PNG to JPG are working with screenshots or photos that have no transparency at all, so this is a non-issue for them. If you are unsure whether your PNG has transparency, just look at it in your file browser. Transparent areas typically show as a checkerboard pattern in preview apps.

For photos, you are looking at 50 to 80 percent smaller, which is a massive difference. I have converted 8MB PNG screenshots of photo-heavy websites down to under 1MB as JPGs. The reason the savings are so dramatic is that PNG uses lossless compression which preserves every pixel exactly, while JPG uses lossy compression that intelligently discards details your eye will not notice. The savings vary by content though. A PNG photograph will compress extremely well as JPG because photos have smooth gradients that JPG handles efficiently. A PNG screenshot with sharp text and solid colors will still be smaller as JPG, but the ratio will be more like 30 to 50 percent. For comparison, TinyPNG can optimize PNGs without converting formats, but you will almost always get a smaller file by switching to JPG entirely. The conversion here uses 92 percent quality by default, which keeps the image looking crisp while delivering serious size reduction.