How to Calculate Audio Bit Rate and File Size (Why 44,100 × 16 Matters)
Uncompressed audio size is plain multiplication: bit rate equals sample rate × bit depth × number of channels, and file size equals bit rate × duration. For stereo CD audio — the 44.1 kHz / 16-bit format standardized in IEC 60908 — that works out to 44,100 × 16 × 2 = 1,411,200 bits per second. Everything else about PCM file size follows from that one line of arithmetic.
The formula, step by step
- Sample rate is how many measurements are taken per second: 44,100 for CD-lineage audio.
- Bit depth is how many bits store each measurement: 16 for CD.
- Channels multiply the whole thing: 2 for stereo, 1 for mono.
So the string "44100 × 16" that people type into search is the first two-thirds of the bit-rate formula. Completing it for stereo:
- 44,100 samples/s × 16 bits × 2 channels = 1,411,200 bits per second, commonly written as about 1,411 kbps or 1.4 Mbps.
- Divide by 8 to get bytes: 176,400 bytes per second.
- Multiply by 60: about 10.6 million bytes per minute of stereo CD-quality audio.
A four-minute track in uncompressed stereo PCM therefore lands in the neighborhood of 42 million bytes. One wrinkle worth knowing: "megabyte" is used in two senses — a decimal million bytes and a binary 1,048,576 bytes — so the same file can be reported with slightly different numbers depending on which convention a given tool uses. The figures above use the decimal sense.
Scaling the formula
Because the relationship is linear, every change scales predictably. Doubling the sample rate doubles the size; moving from 16-bit to 24-bit multiplies size by 1.5; mono halves it. This is why archival masters made to the higher end of the Library of Congress recommended audio formats — which set 44.1 kHz / 16-bit PCM as the floor — occupy several times the space of a CD-resolution file. The meaning of the input numbers themselves is covered in what 44.1 kHz and 16-bit actually mean.
Where compression changes the math
The formula above describes raw PCM, as stored in WAV or AIFF files. Lossless compression breaks the direct link between resolution and size without touching the audio: FLAC, per the Xiph.Org documentation, stores the same PCM samples in less space and decodes them back bit-for-bit, with the achieved size depending on the material — dense, loud content compresses less than sparse or quiet content. How that squares with the word "lossless" is covered in is FLAC really lossless.
Lossy formats abandon the formula entirely. An MP3 or AAC file's size is set by its encoded bit rate — 256 kbps means 256 kilobits per second of file, regardless of the source's sample rate or bit depth — because the encoder discards signal detail to hit that target.
The short version
For uncompressed audio: sample rate × bit depth × channels = bits per second; divide by 8, multiply by seconds, and the file size is known before the file exists. For lossless compression the answer becomes "less than that, same sound." For lossy formats, the bit rate on the label is the whole story.