Complete guide: Split PDF by size

When to split instead of compress

Compression can only go so far, especially for scan‑heavy documents. If you must hit a strict limit (like 20 MB), splitting ensures each part stays under the cap while preserving page order.

Splitting is also useful when recipients prefer smaller files, when a PDF is too large to upload, or when your organization enforces strict attachment policies.

PDFThin lets you choose a target size and returns a ZIP containing ordered parts. This removes the guesswork from manual splitting.

How PDFThin builds size‑safe parts

We estimate the average bytes per page and plan a page range that keeps each part under your target. Each part is optimized and, if needed, lightly recompressed so the size stays consistent.

If a part still exceeds the limit, PDFThin splits it again into smaller chunks. The result is a stable set of files labeled in order (part01, part02, etc.).

You get a ZIP archive with consistent naming, which makes it easy to attach parts in order.

Choosing the right target size

For email attachments, use a preset: Gmail 25 MB, Outlook 20 MB, Outlook.com 25 MB. If your provider is strict, choose a smaller custom target to allow for encoding overhead.

For uploads, set a target that matches the platform limit (for example, 10 MB per file). Splitting helps you avoid failed uploads and repeated retries.

PDFThin keeps the page order intact across parts so you can reconstruct the document easily.

Best practices

Keep the original file as a reference, then share the ZIP of split parts. When sending via email, attach the parts in order and include a short note for the recipient.

If you need a single file instead of parts, try the email‑ready optimizer first. It will only split when compression can’t reach your target.

Start here: Split PDF by size.

Does splitting change page order?

No. Parts are created in order and labeled accordingly.

Can I still compress before splitting?

Yes. PDFThin optimizes each part, and you can also use Email‑ready first.

What output do I get?

A ZIP file containing ordered PDF parts under your target size.

More guides

See Compress PDF for email and Reduce scanned PDF size.

All PDF tools

Browse every PDFThin tool in one place.

Email-ready compression

Shrink PDFs to Gmail/Outlook limits with quality control.

Split by size

Split large PDFs into size-safe parts.

Organize PDF

Merge, rotate, delete, reorder, and split pages.

All PDF guides

Browse every step-by-step PDF guide.

Compress PDF for email (complete)

Step-by-step workflow for Gmail 25MB and Outlook 20MB limits.

Reduce scanned PDF size

Keep text readable while shrinking scanned documents.

Split PDF by size

Create parts that stay under a target MB limit.

Rotate PDF pages online

Fix page orientation for sideways scans or photos.