Audio file size depends on bitrate and duration for compressed formats, or sample rate, bit depth, channels, and duration for uncompressed PCM audio. This guide explains each formula with practical examples for podcasts, music, audiobooks, WAV files, and storage planning.
Audio File Size Formulas at a Glance
Audio file size depends on whether the audio is compressed or stored as uncompressed PCM.
For compressed audio with a known average bitrate:
File Size in Bytes = Bitrate in kbps × 1,000 × Duration in Seconds ÷ 8
For uncompressed PCM audio:
File Size in Bytes = Sample Rate × Bit Depth × Channels × Duration in Seconds ÷ 8
These formulas can also be rearranged to calculate bitrate or available recording time.
Use the Audio File Size Calculator to perform these calculations without converting each unit manually.
How Compressed Audio File Size Is Calculated
Compressed formats reduce the amount of data required to store audio. Common examples include MP3, AAC, Opus, and other codec and container combinations.
When an average bitrate is known, the mathematical size is determined by bitrate and duration.
Step 1: Convert Duration to Seconds
For a 90-minute podcast:
90 × 60 = 5,400 seconds
For a two-hour audiobook chapter:
2 × 3,600 = 7,200 seconds
Step 2: Convert Kilobits to Bits
A bitrate of 128 kbps is treated as:
128 × 1,000 = 128,000 bits per second
Step 3: Multiply by Duration
For 128 kbps audio lasting 5,400 seconds:
128,000 × 5,400 = 691,200,000 bits
Step 4: Convert Bits to Bytes
Eight bits equal one byte:
691,200,000 ÷ 8 = 86,400,000 bytes
The estimated file size is:
- 86.4 MB
- Approximately 82.4 MiB
The actual encoded file may differ slightly because of metadata, container information, encoder padding, and variable bitrate behavior.
Compressed Audio Examples
One Hour at 64 kbps
64 × 1,000 × 3,600 ÷ 8 = 28,800,000 bytes
Estimated size:
- 28.8 MB
- Approximately 27.47 MiB
One Hour at 128 kbps
128 × 1,000 × 3,600 ÷ 8 = 57,600,000 bytes
Estimated size:
- 57.6 MB
- Approximately 54.93 MiB
One Hour at 192 kbps
192 × 1,000 × 3,600 ÷ 8 = 86,400,000 bytes
Estimated size:
- 86.4 MB
- Approximately 82.4 MiB
One Hour at 320 kbps
320 × 1,000 × 3,600 ÷ 8 = 144,000,000 bytes
Estimated size:
- 144 MB
- Approximately 137.33 MiB
Audio Size per Minute and Hour
The following table shows mathematical estimates for constant or average bitrate audio.
| Bitrate | Per Minute | Per Hour |
|---|---|---|
| 32 kbps | 0.24 MB | 14.4 MB |
| 48 kbps | 0.36 MB | 21.6 MB |
| 64 kbps | 0.48 MB | 28.8 MB |
| 96 kbps | 0.72 MB | 43.2 MB |
| 128 kbps | 0.96 MB | 57.6 MB |
| 160 kbps | 1.20 MB | 72 MB |
| 192 kbps | 1.44 MB | 86.4 MB |
| 256 kbps | 1.92 MB | 115.2 MB |
| 320 kbps | 2.40 MB | 144 MB |
These values use decimal megabytes and exclude additional overhead.
How to Calculate Required Audio Bitrate
If a platform or delivery system imposes a maximum file size, rearrange the compressed audio formula:
Bitrate in kbps = File Size in Bytes × 8 ÷ Duration in Seconds ÷ 1,000
Suppose a 60-minute recording must remain within 50 MB.
Convert the values:
- File size: 50,000,000 bytes
- Duration: 3,600 seconds
Calculate the bitrate:
50,000,000 × 8 ÷ 3,600 ÷ 1,000 = 111.11 kbps
The mathematical maximum is approximately 111.11 kbps.
In practice, choose an available setting below that result to leave space for metadata, artwork, and container overhead.
For example, a 96 kbps export would remain below the mathematical 50 MB limit:
96 × 1,000 × 3,600 ÷ 8 = 43.2 MB
How to Calculate Available Audio Duration
When file size and bitrate are known:
Duration in Seconds = File Size in Bytes × 8 ÷ Bitrate in kbps ÷ 1,000
Suppose 250 MB is available for audio encoded at 128 kbps.
250,000,000 × 8 ÷ 128 ÷ 1,000 = 15,625 seconds
Convert the result:
- 260.42 minutes
- Approximately 4 hours, 20 minutes, and 25 seconds
This calculation can help estimate recording time for storage-limited devices, upload limits, course modules, interviews, or audio archives.
What Is PCM Audio?
Pulse-code modulation, or PCM, represents sampled audio without perceptual compression.
A PCM recording stores a sequence of sample values for every audio channel. Its raw data rate depends on:
- Sample rate
- Bit depth
- Channel count
Because these settings normally remain constant throughout a PCM recording, its uncompressed size can be calculated directly.
PCM Audio File Size Formula
The formula is:
PCM Size in Bytes = Sample Rate × Bit Depth × Channels × Duration ÷ 8
The associated PCM bitrate is:
PCM Bitrate = Sample Rate × Bit Depth × Channels
For 44.1 kHz, 16-bit stereo:
44,100 × 16 × 2 = 1,411,200 bits per second
This equals:
- 1,411.2 kbps
- 176,400 bytes per second
A 60-second recording therefore requires:
176,400 × 60 = 10,584,000 bytes
The raw PCM data is approximately:
- 10.584 MB
- 10.094 MiB
A WAV file containing the PCM data will usually be slightly larger because it also contains a header and may include metadata or other chunks.
Common PCM Size Examples
44.1 kHz, 16-bit Mono
One minute:
44,100 × 16 × 1 × 60 ÷ 8 = 5,292,000 bytes
Estimated raw size:
5.292 MB per minute
44.1 kHz, 16-bit Stereo
One minute:
44,100 × 16 × 2 × 60 ÷ 8 = 10,584,000 bytes
Estimated raw size:
10.584 MB per minute
48 kHz, 24-bit Stereo
One minute:
48,000 × 24 × 2 × 60 ÷ 8 = 17,280,000 bytes
Estimated raw size:
17.28 MB per minute
96 kHz, 24-bit Stereo
One minute:
96,000 × 24 × 2 × 60 ÷ 8 = 34,560,000 bytes
Estimated raw size:
34.56 MB per minute
Doubling the sample rate doubles the uncompressed data size when all other settings remain unchanged.
How Sample Rate Affects File Size
Sample rate is the number of samples recorded per second for each channel.
Common sample rates include:
- 8,000 Hz
- 16,000 Hz
- 22,050 Hz
- 44,100 Hz
- 48,000 Hz
- 88,200 Hz
- 96,000 Hz
- 192,000 Hz
If sample rate doubles while bit depth, channels, and duration remain unchanged, uncompressed size doubles.
For example, compare 48 kHz and 96 kHz stereo PCM with the same bit depth:
96,000 ÷ 48,000 = 2
The 96 kHz version contains twice as many samples and requires twice as much raw sample storage.
For compressed formats, changing sample rate does not always produce a proportional change in final file size when the total encoded bitrate remains fixed.
How Bit Depth Affects File Size
Bit depth represents the number of bits used for each sample in each channel.
Common settings include:
- 8-bit
- 16-bit
- 24-bit
- 32-bit
For uncompressed audio, file size changes in direct proportion to bit depth.
A 24-bit file requires 1.5 times the raw sample data of a 16-bit file:
24 ÷ 16 = 1.5
A 32-bit file requires twice the raw sample data of a 16-bit file:
32 ÷ 16 = 2
The precise storage used by some formats can also depend on sample containers, floating-point storage, alignment, and application behavior.
How Channels Affect File Size
Channel count multiplies the amount of uncompressed sample data.
Typical configurations include:
- Mono: 1 channel
- Stereo: 2 channels
- 5.1 surround: 6 channels
- 7.1 surround: 8 channels
At identical sample rate, bit depth, and duration:
- Stereo uses twice the raw data of mono.
- Six-channel audio uses six times the raw data of mono.
- Eight-channel audio uses eight times the raw data of mono.
Compressed codecs may use tools that take advantage of similarities between channels. For compressed audio, the total selected bitrate remains the primary mathematical factor in file size.
WAV Is a Container, Not a Single Compression Method
WAV commonly contains uncompressed PCM audio, which is why WAV files are often associated with large file sizes.
However, WAV is a container. The extension alone does not prove that the contained audio uses uncompressed PCM.
To estimate a file accurately, identify:
- The contained audio format
- Sample rate
- Bit depth or sample format
- Channel count
- Duration
- Whether compression is used
For ordinary PCM WAV planning, the PCM formula provides a close estimate before header and metadata overhead.
Lossy vs. Lossless vs. Uncompressed Audio
Lossy Compression
Lossy codecs reduce file size by discarding information according to a codec’s design.
Examples can include MP3, AAC, and Opus.
For a known average bitrate, use the compressed audio formula.
Lossless Compression
Lossless codecs reduce storage without discarding the decoded audio information.
FLAC is a lossless audio codec. Its final size depends on how effectively the source can be compressed, so it cannot be predicted exactly from duration alone without assuming a compression ratio or knowing the resulting average bitrate.
Uncompressed Audio
Uncompressed PCM stores sample values without codec compression.
Its raw size follows directly from sample rate, bit depth, channels, and duration.
Constant Bitrate, Average Bitrate, and Variable Bitrate
Constant Bitrate
Constant bitrate aims to maintain approximately the same data rate throughout the file.
The standard bitrate-and-duration formula generally produces a close estimate.
Average Bitrate
Average bitrate describes the mean data rate across the complete file.
If the final average is known, it can be used in the same formula.
Variable Bitrate
Variable bitrate allocates different amounts of data to different parts of the recording.
Simple passages may require less data, while complex passages may receive more.
A VBR file cannot be predicted exactly from a nominal quality setting alone. Use its expected average bitrate for planning and allow additional margin when a strict file limit applies.
Podcast Storage Planning Example
Suppose a podcast publishes eight 75-minute episodes per month at 128 kbps.
One episode:
128 × 1,000 × 4,500 ÷ 8 = 72,000,000 bytes
One episode is approximately 72 MB.
Eight episodes:
72 MB × 8 = 576 MB
One year:
576 MB × 12 = 6,912 MB
The published compressed files require approximately 6.912 GB per year.
Real production storage may be much larger because a podcast workflow can also contain:
- Multitrack recordings
- Uncompressed source files
- Edited sessions
- Alternate exports
- Artwork
- Transcripts
- Backups
Audiobook Storage Planning Example
Suppose an audiobook contains 12 hours of finished audio encoded at 96 kbps.
Convert duration:
12 × 3,600 = 43,200 seconds
Calculate size:
96 × 1,000 × 43,200 ÷ 8 = 518,400,000 bytes
Estimated compressed size:
- 518.4 MB
- Approximately 494.38 MiB
Dividing the audiobook into chapters does not significantly change the amount of encoded audio data, although every file can add some container and metadata overhead.
Music Library Example
Suppose a music collection contains 1,000 tracks averaging four minutes each at 256 kbps.
Total duration:
1,000 × 4 = 4,000 minutes
Convert to seconds:
4,000 × 60 = 240,000 seconds
Calculate size:
256 × 1,000 × 240,000 ÷ 8 = 7,680,000,000 bytes
Estimated size:
- 7.68 GB
- Approximately 7.15 GiB
Embedded artwork and metadata can increase the total.
Recording Project Example
A two-hour stereo PCM session uses:
- 48 kHz sample rate
- 24-bit depth
- 2 channels
- 7,200 seconds
Calculate the raw size:
48,000 × 24 × 2 × 7,200 ÷ 8
File Size = 2,073,600,000 bytes
The raw audio is approximately:
- 2.074 GB
- 1.931 GiB
A multitrack project with eight separate mono tracks at the same settings would contain the equivalent of eight channels of raw sample data:
48,000 × 24 × 8 × 7,200 ÷ 8
File Size = 8,294,400,000 bytes
This is approximately 8.294 GB before project files, waveform caches, edits, and backups.
MB vs. MiB and GB vs. GiB
Decimal and binary storage units are different.
Decimal units use powers of 1,000:
- 1 KB = 1,000 bytes
- 1 MB = 1,000,000 bytes
- 1 GB = 1,000,000,000 bytes
Binary units use powers of 1,024:
- 1 KiB = 1,024 bytes
- 1 MiB = 1,048,576 bytes
- 1 GiB = 1,073,741,824 bytes
A file containing 1,000,000,000 bytes is:
- 1 GB
- Approximately 0.931 GiB
Storage manufacturers, operating systems, applications, and upload services may display capacities differently. Use the exact unit specified by the destination whenever possible.
Why the Actual File Size May Differ
Calculated results estimate audio data based on the selected inputs.
Actual files may be larger or smaller because of:
- Variable bitrate
- Container headers
- Metadata
- Embedded cover artwork
- Chapters
- Encoder padding
- Codec delay
- Error-correction data
- Additional streams
- Sample container alignment
- Application-specific chunks
When a hard file-size limit applies, leave a safety margin instead of encoding directly at the mathematical maximum.
Common Audio File Size Mistakes
Forgetting to Convert Minutes to Seconds
Bitrate is measured per second, so duration must be converted to seconds before applying the formula.
Forgetting to Divide Bits by Eight
Bitrate is normally expressed in bits, while file capacity is expressed in bytes.
Mixing Decimal and Binary Units
MB and MiB are not interchangeable. Confirm which definition the target platform uses.
Applying the Compressed Formula to PCM
PCM size must account for sample rate, bit depth, and channels.
Applying the PCM Formula to Compressed Audio
For a compressed file with a known average bitrate, use bitrate and duration instead of multiplying the source PCM settings.
Assuming Every WAV File Is Uncompressed
WAV is a container and may contain formats other than ordinary uncompressed PCM.
Ignoring Multiple Files
Multiply the per-file result by the number of episodes, tracks, chapters, or recordings.
Treating a VBR Quality Setting as an Exact Bitrate
A VBR quality level does not necessarily produce the same average bitrate for every recording.
Audio Storage Planning Checklist
Before estimating storage, confirm:
- Whether the audio is compressed, lossless, or uncompressed
- Average bitrate for compressed audio
- Sample rate for PCM audio
- Bit depth or sample format
- Channel count
- Duration per file
- Number of files
- Decimal or binary storage units
- Container and metadata overhead
- Backup requirements
- Source and project files
- Alternate exports
- Expected future growth
Frequently Asked Questions
How large is a one-hour 128 kbps audio file?
Approximately 57.6 MB or 54.93 MiB before metadata and container overhead.
How large is a one-hour 320 kbps audio file?
Approximately 144 MB or 137.33 MiB.
How large is one minute of 44.1 kHz, 16-bit stereo PCM?
The raw sample data is approximately 10.584 MB.
Does stereo double compressed file size?
Not when the total encoded bitrate remains the same. A 128 kbps stereo file and a 128 kbps mono file have approximately the same mathematical size.
For uncompressed PCM, stereo uses twice the raw data of mono when all other settings remain unchanged.
Can FLAC size be calculated exactly?
Not from duration and PCM settings alone. FLAC size depends on how efficiently the source audio compresses. Use the resulting average bitrate or an assumed compression ratio for an estimate.
Why is the WAV file slightly larger than the PCM calculation?
The PCM calculation measures raw sample data. A WAV file also includes a header and may contain metadata or other chunks.
Does changing the file extension reduce size?
No. Renaming an extension does not re-encode the audio. The content must be converted using an appropriate encoder.
Should required bitrate be rounded up or down?
When a strict maximum file size applies, select an encoder bitrate at or below the calculated maximum and leave room for overhead.
Is data sent to OutputMath?
No. The calculator runs locally in the browser. Entered values and calculation history are not uploaded for processing.
Final Takeaway
Compressed audio size is primarily calculated from average bitrate and duration:
Compressed Size = Bitrate × Duration ÷ 8
Uncompressed PCM size is calculated from sample rate, bit depth, channels, and duration:
PCM Size = Sample Rate × Bit Depth × Channels × Duration ÷ 8
Use consistent units, distinguish MB from MiB, and leave room for headers, metadata, and variable bitrate differences.
Use the Audio File Size Calculator to calculate compressed size, PCM/WAV size, required bitrate, available duration, multiple-file totals, and storage capacity.