How to Calculate Audio File Size

Why does one minute of CD-quality stereo take up 10.58 MB on one screen and 10.09 MB on another? Both numbers are right. They measure the same 10,584,000 bytes with two different kinds of megabyte.

Audio size follows one simple rule, and you can work it out with a phone calculator. This guide shows the formula, a five-part method, and how compressed formats change the answer.

How Is Uncompressed Audio File Size Calculated?

Multiply sample rate by bit depth, channels, and length in seconds, then divide by 8. The result is the file size in bytes for uncompressed PCM audio, such as a WAV or AIFF file.

Each input has a plain meaning. The sample rate is how many snapshots of the sound are taken each second. The FADGI glossary explains that rates above 40 kHz can capture sound up to 20,000 Hz.

Bit depth is how many bits store each snapshot. Channels count the separate audio streams, so stereo has two and mono has one. The final divide by 8 turns bits into bytes, because one byte holds 8 bits.

Drop the seconds from the formula and you get the bitrate. CD audio runs at 44,100 x 16 x 2, or 1,411,200 bits per second. That is 1411.2 kbps, and it never changes during the file.

Every input scales the size in a straight line. Double the sample rate and the file doubles. Move from 16-bit to 24-bit and the file grows by exactly 1.5 times. No other factor changes an uncompressed total, so the result is exact rather than an estimate.

Five Moves From Recording Settings to Megabytes

Here is the hand method, using a 45-minute interview recorded at 48 kHz, 24-bit, in mono. These are typical settings for spoken audio that will sit under video.

1. Read the settings. Find the sample rate, bit depth, and channel count in your recorder or export menu. Write 48 kHz as 48,000, not 48.
2. Find the bitrate. Multiply 48,000 x 24 x 1 to get 1,152,000 bits per second. That is 1152 kbps.
3. Convert the length to seconds. Forty-five minutes times 60 gives 2,700 seconds. Use seconds, because the sample rate counts per second.
4. Multiply and divide by 8. 1,152,000 x 2,700 / 8 gives 388,800,000 bytes. This is the exact size of the audio data.
5. Pick your unit. Divide by 1,000,000 for 388.8 MB, or by 1,048,576 for 370.79 MiB. Say which one you used.

The same interview in stereo doubles to 777.6 MB. A real WAV file also carries a small header, so the file on disk runs a few bytes larger than the audio data.

Why Does the Same File Show Two Different Sizes?

Two definitions of a megabyte are in daily use. A decimal megabyte is 1,000,000 bytes, while a binary mebibyte is 1,048,576 bytes. The same file looks about 4.6 percent smaller in binary units.

NIST lists both units side by side. The binary prefixes kibi, mebi, and gibi were approved by the IEC in December 1998 to end the confusion. Many programs still label binary values as “MB,” which keeps the mix-up alive.

That is why the 10.1 figure for a minute of CD audio is really 10.09 MiB. Measured in decimal units, the same file is 10.58 MB. Neither number is wrong, but mixing them in one plan causes errors.

The gap grows with each prefix. One gibibyte is 1,073,741,824 bytes, about 7.4 percent more than a decimal gigabyte. Our guide to data storage units from KB to TB covers the full ladder.

Bitrates avoid this problem. The FADGI glossary defines kbps as powers of ten, so 1 kbps is exactly 1,000 bits per second. Keep bitrate math decimal, then convert only the final byte count. Plan a whole project in one unit from start to finish, and label every total you write down.

How Do Compressed Formats Change the Math?

Compressed files are sized by their bitrate, not their sample settings. Multiply the bitrate in bits per second by the length in seconds, then divide by 8. The sample rate and bit depth drop out of the math.

A 320 kbps MP3 uses 320,000 x 60 / 8, or 2,400,000 bytes per minute. That is 2.4 MB. At 128 kbps, the same minute is 0.96 MB, and a three-minute song is 2.88 MB.

Compare that with the CD original. A three-minute song in CD stereo is 31.75 MB, which is 4.41 times the 320 kbps version. Lossy formats get there by discarding detail, so the savings come at a cost in fidelity.

Why Lossless Sizes Are Hard to Predict

Lossless formats such as FLAC decode to audio that is bit-for-bit identical to the source. They save space by predicting each sample from the ones before it and storing only the small error.

Quiet, sparse music predicts well and shrinks a lot. Dense, loud, or noisy music predicts poorly and shrinks less. Use the uncompressed size as the upper limit and check a real export for the actual figure. Video follows the same bitrate logic, as our guide to estimating video file size and bitrate explains.

Traps That Skew an Audio Size Estimate

Most bad estimates come from five small unit errors, not from the formula itself. Each one below throws the answer off by a large, fixed factor.

Surround sound shows how fast channels add up. One minute of 5.1 audio at 48 kHz and 24-bit is 51.84 MB, three times the stereo size. An hour of 48 kHz, 24-bit stereo is 1,036.8 MB, just over 1 GB.

Try it with your own session: enter your settings in the audio file size calculator and compare its result with your hand math.

Audio File Size: Frequently Asked Questions

Sources and Further Reading

This article explains storage math for uncompressed and compressed audio. Real files add small headers and metadata, so check an actual export for exact sizes. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated September 27, 2026.