PDF to JPG quality and file size, explained
A JPG made from a PDF page is a compact image of that page. It is not a lossless copy. Knowing what JPG does well — and where it gives up detail — helps you choose a sensible resolution.
JPG is lossy by design
JPG keeps files small by storing an approximation of the image. It gives up detail the eye is unlikely to miss, especially in smooth colour and photographs. On sharp edges — small text, thin lines, diagrams — the approximation can show as slight softness or faint halos around letters when you zoom in.
Why two pages of the same size can differ so much
- Photo-heavy and scanned pages are full of texture. JPG is designed for this kind of content.
- Text and line pages are mostly white with sharp dark edges. At normal zoom they look clean, and the file size depends heavily on how many pixels you asked for.
Because the content decides so much, the size of a JPG cannot be promised in advance — it can be smaller or larger than the PDF it came from. The size of the result depends on each page’s content and dimensions, the resolution you choose and how many pages you save.
Resolution and quality are two different settings
- Resolution (dpi) decides how many pixels the page is drawn with. More pixels means more detail and a larger file. Choosing 96, 150 or 300 dpi compares the three options.
- JPG quality decides how strongly those pixels are compressed.
In PDF to JPG, JPG quality is preset: you choose the resolution, and every export uses the same quality setting. There is no quality percentage to pick. Your browser does the JPG encoding, so the same page can end up a slightly different number of bytes in different browsers.
Practical suggestions
- For sharing and reading on screens, the default 150 dpi is a good starting point.
- For small print or fine drawings you will zoom into, use 300 dpi.
- If a file is too large to send, try 96 or 150 dpi before anything else.
- Saving as JPG involves some compression. If compression marks around edges matter for your use, keep the PDF; this tool produces JPG only.
- Keep the original PDF. A JPG is an image of the page, not a replacement for the document.