Is there any size limit on the files that users can upload to my Google Drive™ through DriveUploader?

There is no upload size limit. The only technical limit is available disk size on your Google Drive™ account. Google offers a variety of Google Drive™  size plans up to the unlimited plan.

However, if you need to set a size limit for uploaded files which people can upload, you can do that in your web application which is using the DriveUploader via the JavaScript API. Here you can see the Filtering files example.

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