How to Split a PDF by Size for Upload and Email Limits
Published by PDFToolz · Updated · Technical references listed below
To split a PDF for an upload size limit, find the largest file the site or mail service accepts, such as 25 MB for Gmail or 12 MB for a USCIS evidence file, and cut the PDF into parts that each stay under it. PDFToolz Split PDF by Size does this in your browser. It saves each candidate part, measures its real size and starts a new part when the next page would push it over. If the receiver accepts only one file, compress the PDF to the limit instead.
This guide lists the published limits for Gmail, Outlook, USCIS and federal court e-filing as of October 2026. It shows how to split a PDF into smaller files by size or by page count, how to choose between splitting and compressing, and what to do when a single page is over the limit.
Why a PDF is too large to upload
Most of a PDF's size comes from images. A 40-page report exported from Word is often under 1 MB, while the same 40 pages scanned in color at 300 DPI can pass 40 MB. Text and vector drawings take little space. Photos, scans and embedded fonts take a lot.
Upload forms and mail servers check the size before they read anything else, and they reject a file over the cap. Upload portals usually count each file. Email counts the whole message, so three 10 MB attachments fail a 25 MB limit just as one 30 MB file does.
- Scanned pages saved in color at 300 DPI or more.
- Phone photos placed into a document at full camera resolution.
- Several PDFs merged into one, each bringing its own copy of the same fonts.
- Files saved many times with incremental updates, which keep old versions inside the file.
Upload and email size limits in 2026
Each service sets its own cap and can change it at any time. These are the limits the services publish as of October 2026. Check the note next to the upload button as well, because a single form can set a lower cap.
| Destination | Limit | What it counts |
|---|---|---|
| Gmail, personal account | 25 MB | All attachments in one message. Gmail replaces a larger attachment with a Google Drive link. |
| Gmail, work or school account | Set by the Google Workspace admin | Ask your admin for the number. |
| Outlook.com | 20 MB | The attachments and the message text together. |
| Outlook with a work Exchange account | 10 MB by default | Your organization can raise or lower it. |
| USCIS online account | 12 MB | Each evidence file. PDF, JPG or JPEG, and TIFF for some forms. Files must not be encrypted or password protected. |
| US federal court CM/ECF | Set by each court | The Western District of Washington allows 100 MB per document or attachment. Check your own court's CM/ECF page for its cap. |
Email makes attachments bigger in transit
Email sends attachments as base64 text. Base64 turns every 3 bytes of the file into 4 characters and adds a line break every 76 characters, so the attachment grows by about 37%. A 20 MB PDF becomes about 27 MB on the way. Some mail servers measure that encoded size against their limit, so a part just under the cap can still bounce.
Leave room for the encoding. Split at 18 MB for a 25 MB Gmail limit, which encodes to about 24.6 MB, and at 14 MB for a 20 MB Outlook.com limit. Upload portals receive the file as it is, so you can split much closer to their stated limit.
Split or compress a PDF that is too large
Both fixes make the upload fit, but they change different things. Compression keeps one file and lowers image quality. Splitting keeps every page at full quality and gives you several files.
| Situation | Better fix | Why |
|---|---|---|
| The form takes one file only | Compress PDF to Size | A second part has nowhere to go. |
| The email, portal or court allows several files | Split PDF by Size | Every page keeps its original quality. |
| Scans of signatures, stamps or small print | Split PDF by Size | Compression blurs fine detail first. |
| A text PDF slightly over the limit | Compress PDF | The Light level rewrites the file structure without touching the pages, and that is often enough. |
| Far over the limit with one upload slot | Delete pages, then compress | Pages the receiver doesn't need take space for nothing. |
| One page is over the limit on its own | Compress that part | A split can only cut between pages. |
How to split a PDF by size, step by step
PDFToolz Split PDF by Size works in Chrome, Edge, Firefox and Safari on Windows, Mac, iPhone and Android. The PDF is read on your device and never uploaded, so a passport scan or a medical record stays with you. There is no account, watermark or page cap.
- Open Split PDF by Size and add the PDF. The tool shows the file size and roughly how many parts to expect.
- Pick the maximum size per part. The presets are 5, 10, 20 and 25 MB, plus Email, which makes 18 MB parts for a 25 MB mail limit. Choose Custom to type another limit, such as 12 MB for USCIS or 500 KB for a strict form. The smallest size it accepts is 100 KB.
- Run the split. Each part takes as many pages as fit under the limit, in their original order.
- Download the ZIP. The parts are named after the original file, such as passport-scan-part-1.pdf and passport-scan-part-2.pdf.
- Unzip the download. On an iPhone or iPad, tap the ZIP in the Files app to expand it.
- Attach or upload the parts in order.
How the size split decides where to cut
Page sizes can't simply be added up. A font or image used on several pages is stored once per file, so 10 pages are rarely 10 times the size of 1 page. Each part also needs its own copy of the fonts its pages use.
So the tool builds real parts and measures them. It guesses a page count from the average page size of your file, saves that many pages and checks the result. If the part fits, it doubles the count until a part is too big. Then it halves the gap between the longest part that fits and the shortest that doesn't. A 40-page part takes about 7 test saves, and the file you download is the exact file that was measured.
Pages are copied into the parts, not redrawn. Text stays selectable, images keep their resolution, and page size and rotation stay the same. If the PDF is already under the limit, you get the original file back unchanged.
Split a PDF into smaller files by page count
If the receiver wants a fixed number of pages per file, or exact sections such as one file per exhibit, use Split PDF instead. Its Every N pages mode cuts the file into equal parts. Its Page ranges mode saves each range you type, such as 1-12, 13-30, as its own PDF.
To reach a size target by page count, work out the average page size first. A 60 MB scan with 120 pages averages 0.5 MB a page, so 40 pages come to about 20 MB. Aim well below the limit, because pages with photos are larger than the average. Split PDF by Size skips this arithmetic by measuring every part.
When one page is bigger than the limit
No splitter can cut a page in half. A high-resolution scan or photo page that is over the limit by itself goes into a part of its own, and the result screen names that page and its size. A PDF with only one page can't be split at all.
Run that part through Compress PDF to Size with the same limit. It first rewrites the file without touching the pages, then re-saves large images as smaller JPEGs, which keeps text selectable. Only if those steps can't reach the target does it turn pages into images, from 150 DPI down to 50 DPI. If many pages are oversized, compress the whole PDF first and then split it.
Name and order the parts for courts and portals
Courts with a size cap ask filers to divide large documents and label each piece. The Western District of Washington, for example, requires a document over 100 MB to be divided into parts of 100 MB or less, labeled like Exhibit 1, Part 1 and Exhibit 1, Part 2.
Parts from PDFToolz end in -part-1, -part-2 and so on. With 10 or more parts, some file lists sort part-10 before part-2, so check the order before you submit.
- Rename each part to what the court or portal expects, such as Exhibit-1-Part-1.pdf.
- Upload the parts in page order, one per slot.
- Remove any open password first. USCIS asks for files that are not encrypted or password protected.
- Keep the full original in case the receiver asks for it.
Split a PDF by size in Adobe Acrobat
Acrobat Pro and Acrobat Standard, both paid, can split a PDF by a maximum file size. The same Split tool also splits by number of pages or by top-level bookmarks.
- Open the PDF and select All tools > Organize pages.
- In the left pane, select Split.
- Open the Split by menu and choose File size.
- Set the maximum size per file.
- Select Output options to pick the folder and file names, then select Split.
What split parts keep and drop
The page content is copied as it is. A few document-level extras don't come along.
- Text, fonts and images look exactly as they did in the original.
- Comments and web links stay on their pages. Links that jump to a page now in another part stop working.
- Bookmarks and document details such as title and author are not copied. To split a book into chapter files that keep their bookmarks, use Split PDF by Bookmarks.
- Fillable form fields may stop working, so fill in and flatten a form before you split it.
- If the PDF opens without a password but blocks printing or copying, the parts are saved without those restrictions. Add a password again with Protect PDF if you need one.
Troubleshooting a split PDF that still won't upload
Most failed uploads after a split come from one of these causes.
- The part is under the limit but the email bounces. Encoding made it bigger. Split again at about 70% of the limit, such as 18 MB for 25 MB, or pick the Email preset.
- The portal says the file is too big although it looks smaller. Some sites count 1 MB as 1,000,000 bytes, while PDFToolz counts 1,048,576. Type a slightly lower custom size, such as 9.5 MB for a 10 MB form.
- One part is far over the limit. It holds a single large page. Compress that part to the limit.
- The portal says the file is damaged or the wrong type. Run the part through Repair PDF and check that the site accepts PDF.
- The split is slow. Each part needs a few test saves, so a file with hundreds of pages can take a minute. The whole PDF is held in memory, so a file of several hundred MB may be too large for a phone.
- The PDF asks for a password to open. Remove it first with Unlock PDF, using the password you know.
Key takeaways
- ✓To split a PDF for an upload limit, pick the limit and cut the file into parts that each stay under it.
- ✓Gmail allows 25 MB per message, Outlook.com 20 MB, USCIS 12 MB per file, and each federal court sets its own CM/ECF cap.
- ✓Email encoding adds about 37% to an attachment, so split at 18 MB for a 25 MB limit.
- ✓Splitting keeps full quality. Compress only when the receiver takes a single file or one page is over the limit alone.
- ✓PDFToolz Split PDF by Size measures every part and runs in your browser, with no upload.
Tools for the job
Frequently asked questions
How do I split a PDF into smaller files by size?
Open PDFToolz Split PDF by Size, pick a maximum such as 10 or 25 MB, or type a custom size, and run the split. Each part takes as many pages as fit under the limit, in order, and all parts download in one ZIP. It is free and runs in your browser.
My PDF is too large to upload. What can I do?
If the site accepts several files, split the PDF by size so each part fits. If it accepts one file, compress the PDF to the limit with Compress PDF to Size, or delete pages the receiver doesn't need. Scans shrink the most, because their size comes from images.
How do I split a PDF to email it under 25 MB?
Pick the Email preset in Split PDF by Size, which makes parts of up to 18 MB, and send each part in its own message. Gmail's 25 MB limit covers all attachments in one message, and email encoding makes files about 37% larger in transit. For Outlook.com, whose limit is 20 MB, type a custom size of 14 MB.
What is the attachment size limit for Gmail and Outlook?
Personal Gmail accounts allow 25 MB of attachments per message, and Gmail replaces larger files with a Google Drive link. Outlook.com allows 20 MB, counting the message itself. Work accounts on Exchange default to 10 MB, and Google Workspace admins set their own limit.
What is the file size limit for USCIS uploads?
USCIS accepts evidence files up to 12 MB each in your online account, as PDF, JPG or JPEG, and as TIFF for some forms. Files must not be encrypted or password protected. Split a longer PDF into parts under 12 MB and upload each part.
Can I split a PDF by size for free on Mac or iPhone, without Acrobat?
Yes. PDFToolz Split PDF by Size runs in Safari, Chrome and other current browsers on Mac, iPhone, Windows and Android, with no install or account. Acrobat Pro and Standard can split by file size too, but both are paid.
Does splitting a PDF reduce its quality?
No. Splitting copies pages into new files without compressing them, so text stays selectable and images keep their resolution. Only compression lowers quality, which is why splitting is the better fix when the receiver accepts several files.
Related terms
Sources and further reading
- Send attachments with your Gmail message from Gmail Help
- Send large files with Outlook from Microsoft Support
- Tips for filing forms online from U.S. Citizenship and Immigration Services
- What is the maximum allowable file size for documents filed in CM/ECF? from US District Court, Western District of Washington
- Split PDFs in Acrobat from Adobe Acrobat Help
- RFC 2045: Multipurpose Internet Mail Extensions (MIME) Part One from IETF
Browse all PDF guides, look up a term in the PDF glossary, or head back to the PDFToolz toolkit.