Facebook post varies in different types, it can be text when you are typing, video, or image. For text, the character limit of the Facebook post is 63,206 while the image size of a Facebook post is 940 x 788 pixels and when you are using video as a Facebook post in the news feed its size is 4 GB Maximum.
For more details read from following link for recommendations of video post on Facebook news feed.
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That is the maximum allowed limit for a post of news feed on Facebook but this isn’t the standard for engagement.
For engagement 50 character posts of Facebook are highly interactive.
For character limit before see more Facebook cuts off 477 characters.