Arithmetic
PDF size estimator
Text is almost free. Images are the whole file. This works out where a document will land, and whether it will clear the limit you have been given.
Adjust the content type first; it matters more than anything else here.
Estimate
Where the bytes actually are
A page of text in a PDF is a few kilobytes. Text is stored as characters plus positions, and it compresses well, which is why a two hundred page book with no pictures can be under a megabyte. If your text-only document is enormous, the cause is almost never the text.
Two things dominate instead. Images, which are stored at whatever resolution was placed rather than the size they appear on the page, so a phone photo scaled down to a thumbnail still costs three megabytes. And embedded fonts, which can add several hundred kilobytes for a family with multiple weights, or several megabytes for a CJK font.
Scanned documents are a separate category: every page is a photograph, so the page count and the scan resolution set the size entirely. The scan size calculator handles that case properly.
Common questions
My PDF is far larger than this says.
Check three things in order: whether the images are at full camera resolution, whether fonts are embedded without subsetting, and whether the file has accumulated revision history from repeated saves. Inspect it to find out which.
How do I get under the limit?
Reduce the images before exporting, which keeps text selectable. Failing that, compress to a target, or split the document.
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