What size should a PDF be? Pick a target that fits where it goes

Why there is no single right size

A PDF is a container. Its size is whatever it carries: typed text and drawings cost almost nothing, pictures cost nearly everything. So “what size should it be” is really 2 questions: where is it going, and what is in it?

The destination gives you a ceiling. The content tells you whether reaching it will hurt. Everything else on this page is those 2 questions answered with numbers.

The ceilings that actually exist

Where it goes	The limit	Aim for
Gmail (personal)	25 MB per message	under 10 MB, at most about 18 MB
Outlook.com	25 MB per message, including the text	under 10 MB, at most about 18 MB
Someone’s work email	set by their company, often lower	under 10 MB
An upload portal (jobs, visas, exams)	the number on the form, often 100 KB to 5 MB	a little under that number
Print shop, archive, legal record	none, or very large	as big as the quality needs

Gmail’s 25 MB is from Google’s Gmail Help page on attachments, and Outlook.com’s 25 MB from Microsoft’s support article on sending limits in Outlook.com, both checked on 11 October 2026. The “aim for” column is lower for a reason: email encodes attachments in a way that adds about a third to their size, so a 24 MB file travels as roughly 32 MB. And you rarely know the receiver’s limit, which is why 10 MB is the target that gets through almost everywhere. The full table by provider is in email attachment size limits, and the strict-number side in portal PDF size limits.

If nobody gave you a limit and the file is going to print or into an archive, there is no target. Keep the full-quality file.

How much a page weighs, measured

These are real outputs from our test files, made on 11 October 2026 with the compressor on this page:

Read it this way:

• Typed text is nearly free. Our 500-page text file is 117 KB in total, under 1 KB a page. Embedded fonts add a one-off cost per file, not per page.
• A clean greyscale scan is small. Our 1-page lease scanned at 200 dpi in grey is 34 KB.
• A colour scan is heavy. Our 10-page lease scanned at 300 dpi in colour, with paper grain, as a scanner app saves it, is 17.6 MB: about 1.8 MB a page. The Web preset brings it to 3.2 MB, the Email preset to 1.7 MB.
• Phone photos are the heaviest. 5 photos from a 12 megapixel camera, one per page, are 14.7 MB. The Email preset makes them 395 KB, about 80 KB a photo.

So a sensible size for a screen is roughly 170 KB to 320 KB per scanned page, and almost nothing per typed page. A 10-page scan at 18 MB is not wrong, it is just a print-quality file sent to a screen.

The 2-question chooser

Question 1: where is it going?

1. Read on a screen (email, a chat, a portal): pick the Email preset (pictures at 110 dpi). Scans stay readable at normal zoom.
2. Read on a screen, zoomed in (a plan, a form with small print, a photo someone will inspect): pick Web (150 dpi).
3. Printed or archived: pick Print (300 dpi), or do not compress at all.
4. A form names a number: type it in Size target instead. The compressor searches all its settings, whatever the preset, keeps the best quality that fits, and tells you which setting it took. A file already under the number comes back untouched.

Question 2: what is in it?

1. Typed text, from a word processor: it is already small. Compressing changes little, and the tool says so.
2. Scans or photos: this is where the size is, and where the presets work. Expect the numbers above.
3. A mix: the pictures set the size. Look at the result’s per-page lines to see which pages carried the weight.

If you cannot tell what is inside, the inspector counts the pictures, shows their share of the file and names the largest one.

Pick the loosest target that passes

Over-compressing has a cost and no benefit. A portal that accepts 2 MB does not treat a 200 KB file better than a 1.9 MB one, but the 200 KB scan has lost most of its detail. Our 10-page scan shows the trade: at a 2 MB target it lands at 1.8 MB with pictures at 110 dpi; at a 200 KB target it gets to 197 KB only at 50 dpi and quality 25, which is the strongest setting there is.

So when you have a limit, type that limit as the target, not a smaller number: the tool already keeps the best quality that fits. When you have no limit, the Email preset is the sensible default for anything read on a screen.

Keep 2 copies when it matters

Compression that shrinks pictures is one-way: the detail it drops does not come back. For anything you may need again (a signed contract, a medical record, a scanned certificate), keep 2 files:

1. The original, full quality, for your records and for printing.
2. The travel copy, compressed for the destination, named so you can tell them apart. The compressor adds -compressed to the name for that reason.

When to leave it alone

If nobody set a limit and the file sends fine, do nothing. Compression is a fix for a file that does not fit, not a habit to run on every PDF. A typed document cannot shrink much anyway: the compressor returns it unchanged and says the size is text, fonts and drawings, which it keeps as they are.

And if a scan must hit a tiny limit, compression is not always the right lever. Our 10-page colour scan does not get under 100 KB at any setting; 5 of its pages do. When the number is that small, send fewer pages: how small a PDF can get covers the floor, and the units guide covers what “100 KB” means to a portal.

Everything here runs on your device; the file is never uploaded, so you can try a setting, look at the result, and try another without anyone else seeing it.