what's BITRATE when exporting h264 1920x1080

After exporting, you can open the video in Quicktime Player and press Command-I.

Before exporting, there is no way of knowing exactly, as it depends not just on duration and frame size, but on the actual content of the video.

FCP does not provide finer control of bit rate, but it seems to export in rather high bit rate.

Unless you find that the result is not satisfactory, there is no reason to worry much about getting a higher bit rate.

It really depends on the content, but higher bit rate does not necessarily mean higher quality.

If you are not satisfied with the result, you may try exporting in ProRes, and then use either Compressor or HandBrake to make an H264, with perhaps higher bit rate, but I don't think it is worth the trouble.

Can you elaborate on why you are so concerned with bit rate?

From memory I believe the average bit rate for 1080p projects is around 20 mbps which as Louis said is generally more than enough.

You can often drop to 10 mbps or even lower without sacrificing quality.

If you have Compressor you will be able to create your own preset with your chosen bit rate.

Surprisingly, iMovie has a custom slider in the export section that allows you to specify an exact bit rate so it is rather strange that FCP X doesn't have one.

The range goes from 3.333 mbps to 26.667 mbps.

Just try it. A few years ago I did a quick test with FCP exports with 1920x1080 25 fps H.264.

Format: Apple Devices m4v at about 10.15 Mbit/s.

Format: Computer mp4 at about 19.76 Mbit/s.

Format: Web Hosting mov at about 14.95 Mbit/s.

I couldn't readily see any quality differences with the source material I then used.