JPG to PDF: How Quality and File Size Are Affected

JPG to PDF is a lossless step only if the tool embeds the JPEG data as it is. A tool that decodes the picture and saves it again adds a second round of JPEG compression, and fine detail can suffer. The file grows by a few kilobytes in the first case, and comparing sizes tells you which case you have.

JPG to PDF: what happens to the JPEG data

A JPG is already compressed with a lossy method; MDN calls JPEG the most widely used lossy format for photographs. A PDF can carry JPEG data inside a page without changing it, and the img2pdf project documents exactly that: JPEG data is embedded directly, with only about 500 to 700 bytes of PDF overhead per image.

A test on 2026-10-24 shows the difference between tools. A 600 by 400 pixel JPG of 13.4 KB became a 14.8 KB PDF with img2pdf 0.6.3, and the image in the PDF kept the JPEG filter (DCTDecode). Pillow 13.0.0 also wrote JPEG data, but its documentation says the PDF encoding is chosen from the image mode and is JPEG for RGB images, so the pixels are encoded again from the decoded picture. For one photo you may not see the difference, but every re-encoding is a lossy step.

JPG to PDF file size

A PDF made by direct embedding is about the size of the JPGs plus a small overhead. In the same test, 30 generated JPG files totalling 457.9 KB became a 472.9 KB PDF, 3.3% larger, in 0.29 seconds. The files were synthetic, so read the percentage as an illustration of the overhead and not as a benchmark for photos.

A PDF far larger than the JPGs suggests the tool converted them to a lossless format. A PDF far smaller suggests it shrank the pictures or compressed them harder. Either way, open the file at 100% zoom and look at an area with fine detail, such as text or hair.

Choose a JPG to PDF method

The method decides who touches your pixels. Built-in print-to-PDF features lay the picture on a paper-sized page, which is convenient for one photo; the steps are in convert JPG to PDF. A set of JPGs needs a tool that accepts a list of files, and convert multiple JPG to PDF covers the order and naming of such a batch. The PNG to PDF Chrome extension lists JPG among its supported formats and processes files inside the extension on your computer; the site does not say whether it re-encodes JPEG data, so run the size comparison above on one of your photos.

Not every JPG should become a PDF. From JPG to PDF lists the cases where the JPG is the better file, and photo to PDF covers phone photos, whose rotation and pixel count need a separate look. The same questions for PNG files are in PNG to PDF.

FAQ

Does JPG to PDF reduce quality?

Not if the tool embeds the JPEG data unchanged. A tool that saves the picture again adds another lossy compression pass.

Why is my PDF bigger than the JPG?

The PDF adds a container around the image. In a test with img2pdf, the overhead was a few kilobytes per file.

How can I check whether my tool re-encoded the JPG?

Compare the file sizes. A PDF close to the JPG size suggests direct embedding, and a big difference suggests the image was processed.