Audio Bitrate Explained: 128 vs 192 vs 320 kbps
When you convert audio you are almost always asked to pick a bitrate: 128, 192, 256 or 320 kbps. The number has a big effect on how your file sounds and how much space it takes, yet it is rarely explained. Here is everything you need to choose confidently.
What is bitrate?
Bitrate is the amount of data used to store one second of audio, measured in kilobits per second (kbps). A 192 kbps MP3 uses 192,000 bits — 24,000 bytes — for every second of sound. More bits give the encoder more room to describe the audio accurately; fewer bits force it to throw away more detail.
For uncompressed audio, bitrate is simple arithmetic: sample rate × bit depth × channels. CD audio is 44,100 × 16 × 2 = 1,411 kbps. Lossy codecs like MP3 and AAC squeeze that down to between roughly 5% and 25% of the original by discarding sounds that human hearing is unlikely to notice — a process guided by a psychoacoustic model.
Calculating file size from bitrate
Because bitrate is data per second, file size is easy to estimate:
size in MB ≈ bitrate (kbps) × duration (seconds) ÷ 8,000
| Bitrate | Per minute | 4-minute song | 1-hour podcast |
|---|---|---|---|
| 64 kbps | 0.48 MB | 1.9 MB | 29 MB |
| 128 kbps | 0.96 MB | 3.8 MB | 58 MB |
| 192 kbps | 1.44 MB | 5.8 MB | 86 MB |
| 256 kbps | 1.92 MB | 7.7 MB | 115 MB |
| 320 kbps | 2.40 MB | 9.6 MB | 144 MB |
| 1,411 kbps (WAV) | 10.6 MB | 42 MB | 635 MB |
What do the common MP3 bitrates sound like?
128 kbps was the standard for early downloads. It is perfectly clear for speech and acceptable for casual music listening, but trained ears may hear “swishy” cymbals or smeared reverb on complex tracks, particularly on good headphones.
192 kbps is a sweet spot. For most people and most music it is very hard to distinguish from the original in blind tests, while files stay about 40% smaller than 320 kbps.
320 kbps is the maximum bitrate the MP3 standard allows. It leaves the most headroom for difficult material and is the right choice when the source is lossless or high-bitrate, or when you are archiving and want to be safe.
Constant vs variable bitrate (CBR vs VBR)
With constant bitrate (CBR), every second uses the same amount of data. It is predictable and universally compatible, which is why our M4A to MP3 converter uses it.
With variable bitrate (VBR), the encoder spends more bits on complex passages and fewer on simple ones (like silence or a solo voice), targeting a quality level rather than a size. VBR often achieves better quality per megabyte, but file size is less predictable and a few very old players display incorrect durations. LAME’s -V0 and -V2 presets are popular VBR settings, averaging around 245 and 190 kbps respectively.
Bitrate isn’t everything
Two other factors matter as much as the number:
- The codec. AAC and Opus are more efficient than MP3, so a 128 kbps AAC file usually sounds better than a 128 kbps MP3. Opus sounds remarkably good at just 64 kbps. Compare codecs in our audio formats guide.
- The source. An MP3 can never sound better than what it was made from. A 320 kbps MP3 converted from a 96 kbps file still sounds like a 96 kbps file — just bigger.
Converting between lossy formats
Converting AAC (M4A), OGG or another MP3 into MP3 is a transcode: the audio is decoded and re-compressed, and each generation discards a little more. To minimise this, follow one rule: choose an output bitrate at least as high as the input bitrate, and preferably one step higher.
- 96 kbps AAC voice memo → 128 kbps MP3
- 128 kbps AAC/MP4 audio → 192 kbps MP3
- 256 kbps iTunes Plus AAC → 320 kbps MP3
- Lossless FLAC/WAV → 320 kbps (or 192 kbps if space matters)
Which bitrate should you choose?
- Podcasts, lectures, audiobooks, voice memos: 128 kbps (mono speech can go even lower).
- Everyday music on phones and in the car: 192 kbps.
- Music from lossless sources, DJ sets, archiving: 320 kbps.
- When storage is very tight: consider AAC at 128 kbps via MP3 to M4A — or keep the MP3 at 128 kbps.
Quick checklist
- Find the source bitrate (most players show it in file info).
- Choose an MP3 bitrate equal to or above it.
- Prefer converting from lossless originals when you have them — see FLAC to MP3 and WAV to MP3.
- Keep your originals; you can always re-encode later.