A single track file of 1MB and 1 minute uses around 136 kbps. And that could be an mp3 file, x264 video file, AAC or whatever. It really doesn't matter, Time * Bitrate = SIZE. Ideally, you wouldn't be constrained by size so instead of going by bitrate it would be better to use the encoding based on quality instead.
The calculator is only useful for when you're constrained in SIZE. For example, you want to fit 1h content in a single layer DVD. A single track content would give you around 10000 kbps to use. That's the value to use when using the encoder, for the final file to be of that size. Again, which codec or what content that actually is, doesn't matter. A single track of 1h content at around 10000 kbps will fit a single layer DVD.