NotebookLM File Size Limit: Prepare Sources That Will Upload

Google Notebook — formerly called NotebookLM, rebranded in July 2026 — enforces a limit on how large each source can be and how many sources a single notebook can hold. When an upload fails or a document appears shorter than expected, one of these limits is usually the cause. Knowing which one tells you exactly how to fix it.

Larger research projects quickly run into these limits, turning a technical constraint into an organizational challenge. Tools like fenbs help by keeping a record of which source belongs in which notebook and where each file was split, so nothing gets lost when you divide a document or spread material across multiple notebooks.

Where to find the current limits

Google updates Notebook's limits as the product evolves. Check the Google Notebook help center↗ (opens in a new tab) for the current figures. Look for the supported sources page, which lists per-source size caps, word-count maximums and the total source count for a single notebook.

Each source type has its own ceiling. A PDF, a Google Doc, a pasted URL, a YouTube link and an uploaded audio file are each measured differently. Checking that page before you upload saves a failed attempt.

File size versus word count

PDF and file-based sources are limited by raw file size. A PDF above the limit will fail to upload and show an error. The fix is to split the file into smaller parts before uploading.

Text-based sources such as Google Docs and pasted text are limited by word count rather than bytes. A document that exceeds the limit will either fail or be silently truncated at the cutoff. To check whether a long document was fully imported, ask Notebook a question about content near its end — if it draws a blank, the source was cut short.

The source count limit

Each notebook can hold only a set number of sources. Once you hit that ceiling, adding a new source requires removing an existing one. For a project with many documents, you will need to plan your notebook structure in advance rather than adding freely.

The usual approach is multiple notebooks: one per topic, chapter or project phase. The trade-off is that Notebook cannot query across notebooks in one session. You need to know which notebook holds the source relevant to each question, so keeping a note of your structure matters from the start.

For details on working within source-count constraints, see notebooklm source limit. For the full range of Notebook limits, notebooklm limits and workflow covers them together.

How to split a document that is too large

For a PDF, use a PDF editor — Adobe Acrobat, Preview on a Mac, or a free web-based splitter — to divide the file at a chapter or section break. Each part should be coherent on its own, so choose split points at natural boundaries rather than arbitrary page numbers.

For a Google Doc, copy the second half into a new document and trim the original. Add a note at the top of each part — "Chapter 1-4" and "Chapter 5-8" — so the scope of each is obvious without opening the file.

• Split at a chapter, section or topic boundary rather than mid-paragraph.
• Keep the title, author and date in both parts so each is identifiable on its own.
• Name both parts consistently: "Report Title Part 1 of 2" and "Report Title Part 2 of 2".
• Note the split point so you know where Part 1 ends and Part 2 begins.

Keeping a source map when you split files

When a report splits into three parts across two notebooks, it is easy to forget which part contains the section you need. A source map — a simple record of what is in each notebook and where each source came from — saves time when you return to the project days later.

fenbs keeps links and project notes together outside any one tool. Add the original document URLs, the names of the split files and the notebook each was added to as Links and listings entries or context notes on the project. A connected assistant can read that map at the start of a session and know exactly where to look.

Audio and video sources

Uploaded audio files and YouTube URLs have separate size and duration limits. A long recording may need trimming or splitting into segments. YouTube videos also require accessible captions — a private video, an age-gated video or a video with captions disabled will not process correctly regardless of its length.

Check the Google Notebook help center for the current audio duration and video requirements. They are listed separately from the PDF and document limits, and they update independently when Google adds new capabilities.

How to do this with fenbs

A research project that spans multiple notebooks and split files benefits from one record outside Notebook that maps the whole structure.

1. Create a free account and add a project for your research.
2. Add a context note listing each notebook and its purpose: what topic or chapter it covers.
3. Under Links and listings, record the original source files or URLs alongside the notebook where each was added.
4. Note any split points so the next person — or your next session — knows where Part 1 ends and Part 2 begins.
5. Before a new session, ask your connected AI assistant to read the project context so it knows which notebook holds the material it needs.

fenbs does not connect directly to Google Notebook, so it will not track uploads automatically. The record you keep is intentional — it is only as accurate as the notes you write.