Quick answer
Audio file size = bitrate × duration ÷ 8. A 128 kbps track of 240 seconds is 3.84 MB (3.662 MiB).
Enter the bitrate in kbps and the duration in seconds. The calculator returns the size in MB and MiB.
Related tools: Video File Size Calculator: File size of video with audio at constant bitrates. Media File Size Calculator: File size of an audio or video stream from its bitrate and duration. Bitrate Calculator: Average bitrate of a file from its size and duration.
How to use the Audio File Size Calculator
- Enter bitrate (kbps) (above 0).
- Enter duration (s) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Bitrate | A number, in kbps | > 0 |
| Duration | A number, in s | > 0 |
Formula and method
Formula
size = bitrate × duration ÷ 8
IEEE-754 double precision; shown to the decimals indicated.
Constant-bitrate estimate; variable bitrate files differ and container overhead adds a little.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Bitrate = 128; Duration = 240.
| Result | Value |
|---|---|
| File size | 3.84 MB |
| In MiB | 3.662 |
Example 2
Inputs: Bitrate = 320; Duration = 3600.
| Result | Value |
|---|---|
| File size | 144 MB |
| In MiB | 137.329 |
Example 3
Inputs: Bitrate = 64; Duration = 1800.
| Result | Value |
|---|---|
| File size | 14.4 MB |
| In MiB | 13.733 |
The first line is the headline result (file size). Below it the audio File Size Calculator lists in MiB, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
The arithmetic
128,000 bits per second × 240 s = 30,720,000 bits ÷ 8 = 3,840,000 bytes = 3.84 MB, which is 3.662 MiB. At 320 kbps the same track is 9.6 MB.
Constant bitrate only
The formula assumes a constant bitrate (CBR); variable-bitrate files vary around the average. Uncompressed CD audio is 1,411 kbps, about 10.6 MB a minute. Metadata adds a little.
How the result changes with bitrate
Holding every other input at the first worked example, this table changes only bitrate. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Bitrate | File size | In MiB |
|---|---|---|
| 64 | 1.92 MB | 1.831 |
| 128 | 3.84 MB | 3.662 |
| 256 | 7.68 MB | 7.324 |
| 512 | 15.36 MB | 14.648 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Bitrate: entering "0" shows "Bitrate must be greater than 0." beside that field and no result.
- Duration: entering "0" shows "Duration must be greater than 0." beside that field and no result.
Choosing between the Audio File Size Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Video File Size Calculator](/technology/video-file-size-calculator/) | video bitrate, audio bitrate and duration | File size |
| [Media File Size Calculator](/technology/file-size-calculator/) | bitrate, bitrate unit and hours | File size |
| [Bitrate Calculator](/technology/bitrate-calculator/) | file size, size unit and duration | Average bitrate |
| [Playback Speed Calculator](/technology/playback-speed/) | hours, minutes and playback speed | New duration |
| [Screen Size Calculator](/technology/screen-size-calculator/) | diagonal, aspect ratio width and aspect ratio height | Screen size |
Background: networking and display
Network speeds are quoted in bits per second and file sizes in bytes, and a byte is 8 bits, so a 100 Mbps link moves at most 12.5 megabytes per second; real throughput is usually below the advertised rate. Pixel density is the diagonal in pixels divided by the diagonal in inches: a 1920×1080 display of 24 inches is about 92 pixels per inch, and a 3840×2160 display of 27 inches about 163.
Assumptions and limitations
- CBR only
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for bitrate and duration to confirm this.
Frequently asked questions
How big is a 3-minute MP3 at 192 kbps?
192 kbps × 180 s ÷ 8 = 4.32 MB for a 3-minute MP3.
What is CBR?
Constant bitrate encoding.
Why MB and MiB?
MB is 1,000,000 bytes; MiB is 1,048,576.
What does the Audio File Size Calculator calculate?
File size of audio at a constant bitrate. It returns File size and In MiB.
What formula does the Audio File Size Calculator use?
size = bitrate × duration ÷ 8. Constant-bitrate estimate; variable bitrate files differ and container overhead adds a little.
What do I need to enter in the audio File Size Calculator?
You enter Bitrate (kbps) and Duration (s).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. CBR only.
What is an example of a audio File Size result?
With bitrate 128 and duration 240, the file size is 3.84 MB.
Related calculators
- Video File Size Calculator — File size of video with audio at constant bitrates.
- Media File Size Calculator — File size of an audio or video stream from its bitrate and duration.
- Bitrate Calculator — Average bitrate of a file from its size and duration.
- Playback Speed Calculator — New duration and time saved at a faster playback speed.
- Screen Size Calculator — Width, height and area of a screen from its diagonal and aspect ratio.
- Download Time Calculator — Time to download a file at a given speed.
- eDPI Calculator — Effective DPI from mouse DPI and in-game sensitivity.
Sources
- SI prefixes (kB = 1,000 B) and IEC prefixes (KiB = 1,024 B); 8 bits per byte
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.