“Split this PDF into pieces under 10 MB each” sounds like a size instruction, but most splitting tools — this one included — work in page counts, not megabytes, because a PDF’s pages aren’t equal-sized building blocks. A page of dense scanned photos can weigh fifty times what a page of plain text does, so “every 20 pages” doesn’t reliably mean “every 10 MB.” Here’s how to actually land under a size limit.
Why splitting doesn’t take a size target directly
Split PDF offers three modes — one file per page, fixed-size chunks (by page count), or custom page ranges. None of them ask for a target file size, because a splitter can’t know a chunk’s final size until after it’s built — page content varies too much to predict from a page count alone. This isn’t a missing feature so much as an honest reflection of how PDFs actually work.
The practical path to a size target
1. Compress first, always. Before splitting anything, run the whole document through Compress PDF. This alone often solves the problem outright — a 40 MB scanned document might drop to 6 MB post-compression, which may already be under your limit without splitting at all.
2. Estimate a rough page count per chunk. Check the compressed file’s total size and page count, divide to get an average size per page, then divide your target limit by that average to estimate how many pages should land under it. This is an estimate, not a guarantee — a chunk containing several image-heavy pages will run larger than one that’s mostly text, even at the same page count.
3. Split using fixed-size chunks at your estimated page count. Split PDF’s chunk mode divides the document into equal groups of pages — set it to your estimated number and download the results as a ZIP.
4. Check each resulting file’s actual size, and re-split any individual chunk that landed over your limit with a smaller page count, since content isn’t evenly distributed through most documents.
When custom ranges work better than even chunks
If you already know visually which pages are the heaviest — a scanned document where the first ten pages are dense photos and the rest is plain text, for instance — custom page ranges let you split unevenly on purpose: a smaller range for the image-heavy section, a much larger range for the light, text-only remainder. This produces more evenly-sized output files than blindly splitting into equal page counts would.
If you only need to get under the limit once
For a one-off submission rather than a repeatable workflow, it’s often faster to just try compressing and splitting into a reasonable number of pieces, check the sizes, and adjust than to calculate precisely — most size-limit situations (email attachments, upload portals) have enough headroom that an approximate split gets you there in one or two attempts.
After splitting
- Merge specific pieces back together if you split more finely than you actually needed
- Compress any individual chunk that’s still over the limit after splitting — a single problem chunk is faster to shrink further than re-splitting the whole document
Ready? Try the free Split PDF tool now — no sign-up, no watermark, and your file is never stored.