Audio Bitrate Calculator
Calculate audio file size from bitrate, or find the bitrate needed to hit a target size.
File Size
Audio file size follows the same simple law that video does: bitrate multiplied by duration determines the size, and bitrate alone determines the quality-versus-size trade-off. The difference is that audio bitrates are small enough that the numbers feel less intimidating — but the same confusions bite, especially the bits-versus-bytes conversion. This calculator turns bitrate and duration into a file size, and works backward to find the bitrate that fits an audio file into a target size, which is exactly what you need when packaging a podcast, an album, or a voice recording for a platform with limits.
How the calculator works
Enter the audio bitrate and the duration, and the calculator multiplies them and converts to a file size, handling the bits-to-bytes division for you. In reverse, give it a target size and a duration and it returns the maximum bitrate that fits. It works for both constant-bitrate estimates and as a planning figure for variable-bitrate encodes, which vary around the average. This is the arithmetic behind why an hour-long podcast at speech-friendly bitrates fits comfortably where an hour of high-bitrate music does not.
The formula
File size (MB) = Bitrate (kbps) × Duration (s) ÷ 8 ÷ 1000
÷ 8 converts bits to bytes
÷ 1000 converts kilobits to megabytes scale
Example: 128 kbps song, 240 seconds (4 min)
128 × 240 ÷ 8 ÷ 1000 = 3.84 MB
Stereo doubles the data of mono at the same quality.As with video, the factor of eight between bits and bytes is where estimates go wrong — bitrate is in kilobits, file size in kilobytes or megabytes. Beyond that, the practical thing to know is how bitrate maps to purpose: speech is perfectly clear at 64–96 kbps because the human voice occupies a narrow frequency range, while music needs 192–320 kbps to reproduce the full spectrum without audible compression artifacts. Using a music bitrate for a podcast wastes half the file size; using a speech bitrate for music makes it sound flat.
What to know about audio bitrate
- 1Match bitrate to content: speech needs far less than music. A spoken podcast is transparent at 64–96 kbps because the voice covers a narrow frequency band, while music needs 192–320 kbps to capture the full range cleanly. Encoding a podcast at music bitrates just doubles the file for no audible gain, and podcasting at speech bitrates keeps episodes small and fast to download.
- 2Above about 256 kbps, most listeners cannot hear the difference. The jump from 128 to 256 kbps is often audible on good equipment, but 256 to 320 is a diminishing return that most people cannot distinguish in a blind test. Unless you are archiving or mastering, 256 kbps is usually the practical ceiling worth paying file size for.
- 3Stereo doubles the data of mono at the same quality. Two channels carry twice the information, so a stereo file is roughly double a mono one at the same bitrate. For a spoken podcast, mono is often the right choice — it halves the file with no meaningful loss, since a single voice gains nothing from stereo separation.
- 4Modern codecs deliver the same quality at lower bitrates. AAC and Opus sound as good as older MP3 at noticeably lower bitrates — Opus is especially efficient for speech. Choosing a modern codec can cut file size substantially at equal quality, which matters more than fine-tuning the bitrate within an older format.
- 5For lossless or archival audio, bitrate is not the right lever. Formats like FLAC are lossless and their size depends on the audio's complexity rather than a chosen bitrate, so this kind of calculation applies to lossy formats — MP3, AAC, Opus — where you set a bitrate. If you need perfect fidelity, you are trading away the predictable-size benefit that a fixed bitrate provides.
Frequently asked questions
What bitrate should I use for a podcast?
For spoken content, 64–96 kbps is transparent and keeps episodes small, and mono at the lower end is often ideal since a single voice gains nothing from stereo. This is far lower than music needs because the human voice occupies a narrow frequency range that does not require the full spectrum. An hour-long podcast at 96 kbps mono is a small, fast-downloading file; encoding it at music bitrates would double the size for no audible benefit.
What bitrate is best for music?
192–320 kbps for lossy formats, with 256 kbps a sensible sweet spot for most listeners. Music needs far more than speech because it spans the full frequency range and any compression artifacts become audible on good equipment at low bitrates. The jump from 128 to 256 is often noticeable; from 256 to 320 most people cannot tell in a blind test. Above 320, use a lossless format like FLAC if you truly need archival quality.
How do I calculate an audio file's size?
Multiply the bitrate by the duration, then divide by eight to convert bits to bytes and scale the units. A 128 kbps song running 240 seconds is 128 × 240 ÷ 8 ÷ 1000 = 3.84 MB. Stereo at the same bitrate is already accounted for in the bitrate figure. This calculator does the arithmetic and the bits-to-bytes conversion for you, avoiding the factor-of-eight error that makes manual estimates come out eight times too large.
Does stereo really double the file size?
At the same per-channel quality, essentially yes — two channels carry twice the audio information of one. In practice, the stated bitrate usually already includes both channels, so a '256 kbps stereo' file is 256 kbps total. The real decision is whether you need stereo at all: for a spoken podcast, mono at half the bitrate sounds identical and halves the file, since a single voice does not benefit from stereo separation.
Can I make an audio file smaller without losing quality?
Somewhat, by choosing a more efficient codec rather than lowering the bitrate. AAC and especially Opus deliver the same perceived quality as older MP3 at lower bitrates, so re-encoding to a modern codec shrinks the file without an audible loss. Beyond that, lowering the bitrate does trade quality for size, and switching to mono for speech halves the file cleanly. True lossless compression (FLAC) reduces size only modestly and depends on the content.