The MeGUI bitrate calculator is an extremely versatile calculator. It can give video bit rates for all the video types that MeGUI produces and can take differing containers, audio input codec, b-frames and so on into account.
The calculator is divided into four logical sections: Video, Audio, Output, and Result. It's easiest to go through the calculator in that order too.
The bitrate calculator only updates when you click a button or press enter, so that it doesn't get confused by half-entered values. Because of this, if you manually insert a value, you will need to press enter or click a button (such as increasing something by one and then decreasing it) for the calculation to refresh.
Note: The M2TS calculation is a Work in Progress. Also, the quality estimate may require further refinement.
The video section allows you to choose the video properties, such as time and frame rate. These options will be automatically filled in if you load your AVS script first.
- Hours / Minutes / Seconds: You can use these boxes to input the length of your video. If you have an AviSynth script open in the video section of the main window the time for it will already be imported, as will be the frame rate.
- Total Length in Seconds (hidden): Click the clock to switch to this mode (and unhide) to input the length of your movie as seconds.
- Framerate:The frame rate of your video.
- Number of frames: If your video is variable frame rate or you will be using a non-standard framerate, you can simply enter the number of frames here instead. The bitrate calculator bases the rest of the calculations on the value in this box.
- Codec: Choose the video codec as some codecs require different amounts of overhead. The codec can also affect the quality estimate.
- B-frames: If your video will contain b-frames you should check this box. B-frames add a very small amount of overhead - usually it has a difference of under 1kbit/second, but it will still produce a more accurate result.
The audio and extras section allows you to specify any number audio streams or extra data to be accounted for in the muxing process. An extra may be a subtitle or embedded menu data.
- Select: If you have already encoded your audio you can select it with this button to use the exact size of the file and get a more accurate result. This method will automatically select the correct type for you.
- Type: Choose the type of audio you will be using. Usually variable bitrate audio requires extra overhead.
- Bitrate: If you have not yet encoded the audio you can specify the expected/nominal bitrate here as well as the format you will be using with the ' 'Type dropdown menu.
- Add and remove: You can add additional streams like subtitles and other audio streams to calculate.
- Container: The container used will have a large effect on the final bitrate, different containers mixed with different audio and video formats will require different amounts of overhead. The containers present here are determined by mux path finding.
Calculate By 
This section allows you to calculate the video bitrate and total file size. Depending on what you calculate by, the other values will be calculated for you. You can switch between these modes of operation by clicking the radio buttons.
- Video Bitrate: Choose the average video bitrate, simple enter it into the box.
- Bits Per Pixel: Choose the amount of video data used for each pixel. The BPP value is not very useful because the compressibility of video can vary greatly.
- Quality Estimate: Choose the estimated quality of the video calculated using a combination of BPP, complexity, and video codec. Because the compressibility of video can vary greatly, this value is just an estimate.
- Total File Size: Choose from the many common sizes that are stored in the list. You can quickly load a preset or choose a custom value.
If your result is an average bitrate, you can apply it to the current video config by clicking Apply.