How to Split a PDF by File Size So Each Part Fits an Email

The honest starting point

PaperKit Split PDF has no split-by-size mode and no target-size option. It splits by page ranges only: you tell it which pages go into each part. That means splitting by file size is a short calculation plus a check, not a single button. The method below works every time, and it takes only a minute.

Step 1: Check the file size and page count

Find the total file size and the total page count. The file size is shown in your file manager; the page count is shown when you open the PDF in a reader. Both numbers are needed for the estimate.

Step 2: Estimate the size of one page

Divide the total size by the page count. That gives a rough average size per page. It is rough because scanned pages are heavier than text pages, but it is good enough to plan the split — the size check in Step 4 catches any part that comes out too big.

Step 3: Worked example

Take a 60MB PDF with 150 pages, to be sent through Gmail with its 25MB limit. To leave a safety margin, aim for parts of about 20MB rather than 25MB.

• Average page size: 60MB divided by 150 pages equals 0.4MB per page.
• Pages per part: 20MB divided by 0.4MB per page equals 50 pages per part.
• Split plan: pages 1 to 50, pages 51 to 100, and pages 101 to 150 — three parts of about 20MB each.

Each part is comfortably under the 25MB limit, and the safety margin absorbs the fact that some pages are heavier than the average. If your limit is iCloud at 20MB, aim lower still — parts of about 15MB — and recalculate: 15MB divided by 0.4MB per page equals about 37 pages per part, so use ranges of 37 or 38 pages.

Step 4: Split by page ranges, then check each part

Open the Split PDF tool and split by the page ranges from your plan. After downloading each part, check its actual size. If a part is still over the limit, split that part again into smaller ranges — for example, split a 28MB part into two parts of about 14MB each. If every part is under the limit, you are done. Label the parts in order, Part 1 of 3 and so on, and tell the recipient how many parts to expect.

If the pages are very uneven

When a file mixes heavy scanned pages with light text pages, the average can mislead: a part full of scans may come out bigger than planned. That is exactly what the size check is for. Adjust the ranges — fewer pages in the heavy section, more pages in the light section — and check again. Two rounds of checking are normal for an uneven file, and still faster than guessing ranges blindly.

For the wider sending workflow, see The Best Way to Send a Large PDF When Email Says File Too Big and the pillar guide How to Send PDF Files Anywhere: Email Limits, Sharing and Fixes. The recipient can rejoin the parts with Merge PDF, which joins whole files in order.