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Note: This article was partially created with the help of AI. An author reviewed and revised the content as needed. Read more about Microsoft and Responsible AI practices.

When you write Copilot prompts, you can provide Copilot with information or samples  - the source for Copilot to use.  For example, you can ask Copilot in Word: Write a marketing plan outline based on the product features described in this document. But to get the best output from Copilot, it’s important to consider the length of the content you provide to Copilot, as there are limits to the size of documents that Copilot can read at once.

You probably see that there is a 2000-character limit when you type in your prompts to Copilot. But it seems that you can reference documents of any size with Copilot because there are no reminders on file size limits when you do so.

Behind the scenes, however, there is a limit for the size of the document that you can refer to with Copilot. Depending on the type of tasks you give Copilot, there are times that Copilot will focus only on the beginning of the document (up to its limits) and then ignore anything beyond that. For example, when you ask a question about a specific topic in a long document, document length typically will not impact the ability to get a result based on how the Large Language Models (LLMs) reason over the content. But if you ask for a summary of a long document, the task requires the entire document context to inform the output. For the latter case, length limits do come into play and impact output.

For scenarios where the entire document context is needed for Copilot to provide answer, a couple of good rules of thumb on the length of the document you provide to Copilot: 

  • Shorter than 20 pages: Try to keep the length of the document you refer to under 20 pages. This is a comfortable length for Copilot to handle.

  • Around 15,000 words or less: For those who love word counts, aim to stay at or below 15,000 words. This is a sweet spot for Copilot to work effectively.


  • These recommended limits indicate that content is too long for Copilot to fully process. Different languages will have slight variations in these limits, so you may need to adjust the page or word limits based on the language you use.

  • While these page/word limits are currently a good rule of thumb, we are constantly working to expand Copilot's capabilities, and these limits will increase over time. When they do, this page will be updated to reflect any changes.

  • While we are working on functionality that allows you to point Copilot to a specific section or page range in a document, that experience does not exist today.

Keeping documents you provide to Copilot within these size limits helps Copilot read and respond to your documents accurately and effectively. If your document is longer than these limits, Copilot might still be able to help, but it'll focus only on the first part of your document. It would be like reading only the first few chapters of a book and trying to guess the rest (which is what Copilot ends up doing in this case). 

Tips for Longer Documents 

Here are some ways that you can use longer documents with Copilot: 

  • Break It Down: If you have a long document, consider splitting it into smaller documents and providing them to Copilot separately. This way, Copilot can handle each part effectively.

  • Summarize in Parts: For long reports or manuscripts, you can try summarizing them in chunks with Copilot. Today you can do that by copying/pasting chunks into separate documents and summarizing sections separately. This helps Copilot to give you more precise and relevant responses.

When using Copilot, think of it as having a conversation with your friend. You wouldn't discuss a whole encyclopedia at once, right?  Similarly, keep your document references concise and to the point for the best experience with Copilot.

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