Audio File Size Calculator

The audio file size calculator allows you to estimate the storage space required for a recording. By entering the length of your audio and some quality parameters, it can calculate the file size in megabytes. This version supports two types of audio: for compressed files like MP3 or AAC, the size is directly calculated from the bitrate, while for uncompressed files like WAV or AIFF, the size is calculated based on the sample rate, bit depth, and number of channels.

How are audio file sizes calculated?

Any audio file is a sequence of bits played over time. The size of the file comes from multiplying the bit rate (the number of bits transferred per second) by the recording length (in seconds), then dividing by eight to convert the bits into bytes.

For compressed files, data transfer rate is already known and is expressed in kilobits per second when encoding as bitrate.

For uncompressed files the data transfer rate is not stored directly but must be calculated from recording settings. By multiplying sample rate, bit depth and number of channels one gets the bitrate so the same formula can be applied.

Example:

A four-minute composition saved in the lossless CD-quality WAV format requires this amount of data: 44,100 samples are captured per second, with each sample being 16 bits. Stereo uses two channels. The bit rate is calculated by multiplying 44,100 by 16, multiplied by 2, which gives a data size of 1,411,200 bits per second, usually expressed as 1,411.2 kbps. After 240 seconds the total number of bits is 338,688,000, which when divided by eight equals 42,336,000 bytes, or about 42.3 MB.

The same four-minute composition, saved as an MP3 at 320kbps, requires a data size of 320 bytes, calculated by multiplying 240 divided by eight, which leads to 9,600,000 bytes or 9.6MB. Reducing it to 128kbps reduces the file size to just 3.84MB. This is the effect of compression.

Decimal megabytes versus binary mebibytes

There are two methods for calculating megabytes and the results differ. Storage media manufacturers, download services, and macOS use decimal units where one megabyte is exactly 1,000,000 bytes. Windows and many older software use binary units where a unit called a megabyte actually contains 1,048,576 bytes. The correct technical term for this unit is mebibyte.

So a file that shows as 42.3 MB in this tool might show as 40.4 MiB on devices that use binary units. The number of bytes is the same; only the measurement system changes. This calculator displays both results at once, so even seemingly inconsistent numbers can be easily checked.

Bit rate reference table

These values are based on using a constant bit rate mode. At a given bit rate, one minute of audio will always take up the same amount of data regardless of what is actually being recorded, so you can scale this table to any length.

Does the file size change depending on what's in it?

This is not the case with uncompressed audio. Since both silent and loud sections use the same number of samples, a WAV file will always be the same size as long as length and quality are equal. This is similar to how a cassette tape always uses the same amount of tape regardless of what is recorded on it.

For compressed audio it depends on the encoder. For constant bitrate files, the size is predictable because of the constant rate. This is what this tool is based on. For variable bitrate files, louder sections will be allocated more bits and quieter sections less bits so the actual file size may be slightly smaller or larger than the estimate. For lossless formats like FLAC and ALAC, the size can be reduced by about 30 to 60% of the uncompressed audio, with the exact reduction depending on the material and not just predictable from length alone.

Planning with size restrictions in mind

If you need to fit within a particular maximum size limit, such as for email attachments or uploads, open the Size Limit Planner. Enter your target size and it will calculate backwards in two directions: The bitrate that would allow you to stay within the limit at the current length, and the maximum recording time that would keep you within the limit with the current bitrate. In both cases, the relationship between bitrate, length, and size is the same, only the unknown being sought varies.

Note on the sizes shown:

The size reported by the device may differ slightly from the estimate. There is a small fixed overhead for file headers and metadata, and container formats add padding to align data blocks. Also, as mentioned earlier, megabytes are defined differently in decimal and binary systems depending on your operating system. You can use these estimates when planning storage or transferring data, since they're usually very close to the actual values.