From SBG Media:
Media Size Calculator is a simple utility comprised of 4 calculators.
1. Media Size Converter;
2. Duration to Media Size Calculator;
3. Media Size to Duration Calculator;
4. Data Rate Calculator.
Media Size Calculator enables the user to convert file sizes to different units.
You can determine file size based on duration and data rate. Determine a media file's data rate based on its file size and duration. You can also determine the duration of a media file based on its file size and data rate.
Best of all Media Size Calculator is free and does not require Internet access as do other bit calculators out there.