The official limitation is 23,8 Mb - however, we strongly recommend using files of a smaller size (preferably 10 Mb or less), because the files can become much bigger after encoding on Facebook's side.
Here are some helpful tips:
- Downsampling your video to standard web sizes (no HD)
- Compressing video and changing file type from .mp4 to .mov
- Change dimensions of the video down to a smaller size (the perfect dimensions would be 270x480)
- Using MP3s instead of AAC or WAV
- Using optimized JPEGs instead of RAW or PNG24
- Keeping your animated GIF files to less than 10 seconds in duration
Hope that helps!