Why Your Photo PDF Is So Big (and How to Shrink It Below Email Limits)

You merge a handful of photos into one PDF, expecting a file a little bigger than the photos themselves, and the PDF comes out several times larger. Sometimes it even ends up larger than the originals combined. That is not a bug in one particular app. It comes from how photos get placed inside a PDF, and once you know the rule it is easy to avoid.

We measured it with real files, using Magic File Converter to build the PDFs and Magic Image Compressor to shrink the photos first. The numbers below are the actual byte counts from those runs.

The rule: JPEG goes in as it is, everything else goes in lossless

A PDF can hold a JPEG photo directly, without re-encoding it, so the PDF is barely bigger than the photo. PNG and WebP photos are different. In Magic File Converter, JPEG files are embedded as they are, PNG files are embedded as PNG data, and WebP files are first converted to PNG, because the PDF library it uses cannot embed WebP directly. A WebP photo is small because it is stored with lossy compression. Once it is turned into PNG, the same picture is stored without that saving, and the file grows a lot.

What we measured

We took the same three photos (a latte, a kitten and a dahlia, each 1600 pixels wide) in three formats and merged each set into one PDF with default settings.

Photos in	Total size of the three photos	PDF size	PDF compared with the photos
JPEG	745,013 bytes	746,635 bytes	about the same
PNG	5,740,069 bytes	9,657,040 bytes	about 1.7 times bigger
WebP	339,904 bytes	7,376,892 bytes	about 22 times bigger

So a WebP set that is smaller than a single decent photo turned into a 7.4 MB PDF. If your photos come from a website, a messaging app or a screenshot tool, check the file type before merging. Those are the usual sources of PNG and WebP.

→ Shrink your photos first with Magic Image Compressor — free, runs in your browser, nothing is uploaded.

The fix: compress to JPEG first, then merge

Run each photo through Magic Image Compressor with the output format set to JPEG, then merge the results. We did exactly that with the same PNG and WebP sets.

Photos	Merged directly	Compressed first	Saved
3 PNG photos	9,657,040 bytes	615,837 bytes	about 94%
3 WebP photos	7,376,892 bytes	439,189 bytes	about 94%
2 JPEGs, 3000 px wide	2,872,136 bytes	749,304 bytes	about 74%

The last row is a different case. Those JPEGs were already the right format, but they were 3000 pixels wide, a size that many phone photos exceed. Magic Image Compressor's default settings reduced them to 1920 pixels wide, and that resizing is a large part of the 74% saving. The 1600-pixel photos in the first two rows were left at their original size, so their saving came from the format change alone.

This works for photos. For pages with sharp text, such as a scanned form or a screenshot of a document, JPEG compression can leave faint marks around the letters, so check the result at full size before sending it.

How many pages fit in an email?

For personal accounts, Google's Gmail Help page gives the attachment limit as 25 MB. If you go over, Gmail removes the attachment and adds it as a Google Drive link instead. Work and school accounts use a limit set by their administrator, and other mail providers have their own limits, so check your own before relying on the number. We read the Gmail page on October 30, 2026.

Using the average page from our test, a rough count of pages before you hit 25 MB looks like this.

How the PDF was built	Average per page	Pages before 25 MB
WebP photos merged directly	about 2.5 MB	about 10
PNG photos merged directly	about 3.2 MB	about 7
JPEG photos merged directly	about 0.25 MB	about 100
PNG photos compressed to JPEG first	about 0.2 MB	about 120

These are estimates from three sample photos, and your own photos will compress differently. A busy photo takes more bytes than a plain one, so treat the page counts as a rough guide, not a promise.

Step by step

1. Check your file types. If your photos are PNG or WebP, compress them first. If they are JPEG straight from a camera or phone, you may only need to compress them when they are very large.
2. Compress to JPEG. Open Magic Image Compressor, choose JPEG as the output format, and download the result. Several photos come back as one ZIP file, so unzip it before the next step.
3. Name the files in order. A prefix such as 01, 02, 03 keeps the pages in the order you want.
4. Merge into one PDF. Open Magic File Converter, add the compressed photos, choose "to PDF" and download. Our guide on combining photos into one PDF covers this step in more detail.
5. Check the size before you attach it. If the file is still too large, compress again with a smaller image size, or split the set into two PDFs.

Frequently asked questions

Ready to try it? Compress your photos first, then merge them into one PDF. For more on why file types behave so differently, see our guide to compression versus conversion.