Last updated: 2026-07-01

Audio File Size

Uncompressed digital audio stores a fixed number of bits for every sample, on every channel, for the whole duration. That makes its size completely predictable from four numbers: sample rate, bit depth, channel count, and length.

The formula

where $f_s$ is the sample rate (samples per second), $b$ is the bit depth (bits per sample), $c$ is the number of channels, $t$ is the duration in seconds, and $F$ is the file size in bytes. The product $f_s \times b \times c$ is the bitrate — the raw data rate in bits per second. Dividing by 8 converts bits to bytes, since one byte holds eight bits.

Worked example. Three minutes of CD-quality stereo audio (44,100 Hz, 16-bit, 2 channels):

A full 74-minute CD therefore holds roughly 783 MB of PCM audio, which is why the original CD specification settled on these numbers.

Common audio formats

Decimal vs binary units

There are two conventions for size prefixes. Decimal units treat 1 MB as 1,000,000 bytes; binary units treat 1 MiB as 1,048,576 bytes (1,024 × 1,024). Storage vendors and most audio tools report decimal sizes, while some operating systems display binary sizes but still write the label "MB". The 31.75 MB above is about 30.28 MiB. This calculator lets you switch between the two, so the figure you see matches whatever tool you are comparing against.

Why compressed files are smaller

The formula gives the size of raw PCM, which is what a WAV or AIFF file stores. Lossy codecs such as MP3 and AAC analyse the signal and discard detail the ear is unlikely to notice, then encode at a fixed target bitrate — commonly 128 to 320 Kbps. Because that target is far below the 1,411 Kbps of CD PCM, a 320 Kbps MP3 is roughly a quarter of the size, and a 128 Kbps file about a tenth. Lossless codecs like FLAC and ALAC keep every sample but pack it more efficiently, typically reaching 50–70 % of the PCM size with no quality loss.

Header overhead

A WAV file prepends a small header (around 44 bytes) describing the format. For any recording longer than a fraction of a second this is negligible next to the audio payload, so the formula above is accurate for storage planning.

Related estimates

Video uses the same bits-to-bytes reasoning once you know its bitrate — see the Video Bitrate & File Size Calculator. To compare a compressed result against its source, the Compression Ratio Calculator turns the two sizes into a ratio.