Limit to size

I recorded an audio show, and i want to save it as mp3 to a certain size because i will write it to a cd, and the player from my car only “knows” mp3 format (not aac like original-which is considerably smaller). Using standard presets the result is below/above 700mb limit with around 100mb.
Is there a way to force audacity to export to a fixed size?
Win 11 21h2

In the MP3 export dialog set
a) Constant (bit rate)
b) Stereo
c) the rate you want
MP3 export.png

Nope. I want fixed (or around) size, not fixed bitrate.
This must be using variable bitrate, but not such option to specific target (like is happening in premiere pro when exporting a clip)

Not that I know of. If the file is too large you can make it fit by lowering the quality. Why does it have to be exact ?

You have to work out the bit-rate manually.

Size (bytes) = length (seconds) x bit-rate (bytes per second)


  • Target size = 1 MB (1000000 bytes)
  • length = 1 minute 10 seconds (70 seconds)

Rearranging the above formula:

bit-rate (bytes per second) = Size (bytes) / length (seconds)

bit-rate (bytes per second) = 1000000 / 70 = 14285.7 bytes per second

Multiply by 8 for bits per second:
14285.7 bytes per second = 8 x 14285.7 = 114285.6 bits per second

and finally, divide by 1000 for kilobits per second (kbps)
114285.6 bits per second = 114285.6 / 1000 = 114 kbps

The closes standard bit-rate under 114 kbps is 112 kbps, which gives an actual file size of 958 KiB (just under 1 MB).

In short:
bit-rate (kbps) = file size (kB) x 8 / length (seconds)
Which in the above example is:
1000 x 8 / 70 = 114.285714286

Note that VBR bit-rates are approximate and depend on the complexity of the sound. With CBR you can calculate the file size exactly, but VBR will be approximate.