Estimate file size
For constant bitrate, seconds × kbps ÷ 8 gives an approximate size in kilobytes. A sixty-second recording is about 960 kB at 128 kbps, 1,440 kB at 192 kbps or 2,400 kB at 320 kbps. Headers and encoder delay make the actual size slightly different.
Compare using your recording
Start with 192 kbps and listen against the source. Try 128 kbps when size matters, or 320 kbps if you want a higher bitrate. Speech, music, source quality and listening conditions all affect the result; one option is not best for every recording.
A higher number cannot repair the source
Converting a low-quality recording to 320 kbps does not restore missing detail. Re-encoding an MP3 can introduce further loss. Where possible, create your output once from the original recording and keep that original for editing.