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128 vs 320 kbps: which MP3 bitrate to choose, and how big the file will be

128 kbps MP3 runs 0.96 MB a minute; 320 kbps runs 2.40 MB, two and a half times the size. For speech, and for audio pulled off phone videos, 128 kbps is enough — 320 kbps earns its space only when the source is actually good and someone downstream asks for it specifically.

3 min read · Updated 2026-09-16

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MP3 file size per minute, per song and per hour

The app writes MP3 at a constant bitrate, so the size is plain arithmetic: kilobits per second times 1,000, divided by 8 for bytes, times the seconds. Tags and frame headers tack on only a few KB, nothing worth factoring in.

MP3 size by bitrate (1 MB = 1,000,000 bytes)
BitratePer minute3 minutes1 hourIn the app
64 kbps0.48 MB1.44 MB28.8 MBFree
128 kbps0.96 MB2.88 MB57.6 MBFree
192 kbps1.44 MB4.32 MB86.4 MBPro
256 kbps1.92 MB5.76 MB115.2 MBPro
320 kbps2.40 MB7.20 MB144.0 MBPro
WAV / AIFF10.58 MB31.75 MB635.04 MBFree

So, a 3-minute MP3: 2.88 MB at 128 kbps, 7.20 MB at 320 kbps. The same 3 minutes as WAV comes to 31.75 MB, 11 times the 128 kbps file.

Can you hear the difference between 128 and 320 kbps?

On speech, almost never. On music, a few people pick out a difference at 128 kbps in cymbals and reverb tails on good headphones, most don’t. The source matters more than the bitrate either way — no bitrate puts back detail that was never captured to begin with.

A phone video’s sound is already compressed going in. The app pulls it out as AAC (M4A) first, then encodes the MP3 from that, so a 320 kbps MP3 of a phone video just carries the same sound in a bigger file — nothing new added. Reach for 320 kbps when the source is a genuinely good recording and the destination specifically wants a high bitrate.

M4A vs MP3 vs WAV: which is better?

  • M4A: the AAC file the app makes first, so it’s the least processed of the bunch. Plays on Apple devices and most modern players.
  • MP3: a second encode from that AAC. Its whole advantage is compatibility — car stereos, web forms, basically anything.
  • WAV, AIFF, AIFC, CAF: uncompressed 44.1 kHz, 16-bit stereo copies of the AAC step. They earn their size when an editor or a service demands them, never for extra quality.

How to choose the bitrate in the app

  1. Open a video on the Videos tab, or a file through +.
  2. Choose MP3 under Select format; the Quality picker shows up, and only there — other formats carry no bitrate setting at all.
  3. 64 kbps for speech-only, 128 kbps for general use, or 192/256/320 kbps with Pro.
  4. Tap Convert to Audio. In Batch Conversion, that same Quality pick applies to every video in the run.

Shrink an MP3 that is too big

The app doubles as a basic MP3 shrinker too: import a large MP3 with + and re-convert it to MP3 at 128 or 64 kbps. A 1-hour file drops from 144.0 MB at 320 kbps to 57.6 MB at 128 kbps, or 28.8 MB at 64. It’s still a lossy encode on top of a lossy encode, so do it once from the highest-quality copy you have — not over and over, or the loss stacks up.

Questions and answers

Is 128 kbps good enough?
For speech and for audio off phone videos, yes. It’s also the bitrate most uploads and players expect by default. Go higher only when the source itself is good-quality music.
Is M4A better than MP3?
In this app, M4A is the least-processed output — it’s the AAC file every conversion makes first, and MP3 gets encoded again from that. MP3 wins on compatibility, not on quality.
How big is a 1-hour MP3?
57.6 MB at 128 kbps, 28.8 MB at 64 kbps, 144.0 MB at 320 kbps — counting 1 MB as 1,000,000 bytes.
Why can't I choose 320 kbps?
192, 256 and 320 kbps sit behind Pro. Free gives you 64 and 128 kbps, which covers speech and most everyday sharing fine.

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