It really depends on the title. A good rule of thumb is to expect each hour of your audiobook to take up 14 MB once it's Zipped to your device. Here are a couple of examples:
- Master & Commander - 13 hours - 182 MB
- Scourby Old Testament - 55 hours - 770 MB
Pimsleur lessons (and other various language courses) are a bit of an exception, since they typically include long pauses. In this case, you can expect each hour of audio to fit within 12 MB (for example, a 16 hour Pimsleur Comprehensive title will comfortably fit within 190 MB).
