Bitrate is the amount of video data used per second. Raising it can preserve more detail, but only until the source quality and encoder stop benefiting. It does not create detail that the original recording never captured.
A simple size estimate
Approximate size comes from duration multiplied by combined video and audio bitrate. For example, 10 minutes at 8,000 Kbps video plus 192 Kbps audio is roughly 614 MB before a small container allowance. Variable bitrate output may finish above or below the estimate.
Starting points
For ordinary 720p/30 FPS footage, 4,000-7,500 Kbps is a sensible starting range. For 1080p/30 FPS gameplay with motion and interface text, 8,000-15,000 Kbps can be useful. A higher frame rate or unusually detailed footage may need more. Test a short clip before committing to a long export.
Do not upscale blindly
Exporting a 640p source as 1080p increases pixel dimensions, not real captured detail. It may help meet platform requirements or provide a standard frame, but it also increases processing time and potential output size.