We currently have a file size limit of 20MB. Given that most voice messages are encoded with a constant bitrate and a single channel (mono, no stereo), we can calculate the maximum duration of a file using the following equation:
Applying this equation to our 20MB limit and a bitrate of 64 kbps (commonly used by the iPhone recorder app), we arrive at a maximum duration of approximately 43 minutes and 41 seconds. To easily calculate durations for different file sizes and bitrates, you can use our audio duration calculator.