PDF File Size Limits for Email, Chat and AI Tools (2026)

We only print a number when we read it on a vendor page on 8 November 2026. Where a vendor page was not readable to us, the row says so and links to where to look. Third-party blogs disagree with each other and with the vendors on several of these, so we left them out.

For AI tools the number to watch is often not megabytes. A text-heavy PDF can be rejected for length even when the file is small, and a scan with no text may be read differently from a PDF with real text. Read the vendor page for your plan before you plan around a figure.

Email attaches files as text, and that makes them bigger. We base64-encoded a random 3,000,000 byte file with the standard 76-character line breaks. The result was 4,052,632 bytes, about 35% larger. So a PDF that Finder shows as 20 MB can be about 27 MB on the wire.

head -c 3000000 /dev/urandom > test.bin
base64 -i test.bin -b 76 | wc -c
# 4052632

The practical rule from that measurement: for a 25 MB limit, aim for a PDF of about 18 MB or less (25 divided by 1.35 is 18.5). That is our arithmetic from one test, not a figure from Google, and the real overhead varies a little with the mail app. Leave a margin.

Select the file in Finder and press Command-I, or run this in Terminal:

ls -lh report.pdf
du -h report.pdf

Finder shows decimal megabytes, which is what mail services use. Compare against the limit in the same units, and remember the 35% rule above for email.

Work from cheapest to most effort:

1. Re-export from the source app with a lower image quality. Pages has an Image Quality setting in its PDF export.
2. Open the PDF in Preview, choose File > Export and pick the Reduce File Size Quartz filter. Free, one fixed recipe.
3. Use a compressor with presets, so you can step down one level at a time until the file fits.
4. If it still will not fit, send a link instead of an attachment, through Drive, iCloud or similar.

Images are almost always the weight. Our guide to why PDFs are large shows how to confirm that, and compressing a PDF for email covers the email case in detail. For other services see PDF too big to upload.

Smol has five PDF presets: Tiny, Small, Medium, Large and Original. They cap the long edge of images at 600, 900, 1200, 1800 and 2400 pixels, with JPEG quality of roughly 25, 45, 60, 75 and 88. They are pixel caps, not DPI targets, and Original is not lossless. The saving depends on the file, so we give no percentage. Start at Medium, check the size, and step down only if you must.

In one of our fixtures, a 6.52 MB PDF holding a single large smooth photo came out at 53 KB at Medium. Photos with more detail shrink much less. See what each preset does.

For a single PDF headed to an inbox, Preview’s Reduce File Size filter or a lower-quality re-export is usually enough, and it costs nothing. Smol does not split or merge PDFs, so if a file is too large only because it has too many pages, split it in Preview instead. Smol does not OCR either.

Smol is worth $29 (once, one Mac) when you send size-limited files all the time: folders of PDFs, scans mixed with photos, a Finder right-click, and nothing uploaded to a server. See Smol or the best PDF compressors for Mac.