Audio File Size Calculator

Uncompressed digital audio is stored as linear pulse-code modulation, a plain list of amplitude measurements, so its size is fully determined by four numbers. Sample rate fixes how many measurements are taken per second; bit depth fixes how many bits encode each measurement; channel count multiplies the whole stream; and duration multiplies it again. Dividing bit depth by 8 converts to bytes, giving Size equals Duration times Sample Rate times Bit Depth divided by 8 times Channels. Compact disc audio at 44100 Hz, 16-bit, stereo therefore runs 176400 bytes per second, about 10.1 MB per minute. Sample rate is chosen against the Nyquist limit, which says a sampled system can represent frequencies only up to half the sample rate, so 44.1 kHz covers the roughly 20 kHz ceiling of human hearing. Bit depth sets dynamic range at approximately 6.02 dB per bit, giving about 96 dB at 16-bit and 144 dB at 24-bit. Compressed formats break the direct relationship. For constant-bitrate lossy codecs the size is simply bitrate times duration divided by 8, independent of sample rate or channel count, so a 320 kbps MP3 occupies about 2.4 MB per minute whatever the source resolution was. Lossless codecs such as FLAC and ALAC are content-dependent, typically landing between 40 and 60 percent of the original, with dense loud material compressing least. Several caveats apply to any estimate. Variable-bitrate encoders deviate from the nominal figure, container headers and embedded artwork add overhead, and the mebibyte-versus-megabyte ambiguity introduces a 4.9 percent discrepancy at gigabyte scale depending on whether a division uses 1024 or 1000. Multitrack session files scale with track count and can reach tens of gigabytes for a single song at 24-bit and 96 kHz.

The theory arrived decades before the hardware. Harry Nyquist, working at Bell Telephone Laboratories, published the sampling relationship underlying digital audio in 1928, and Claude Shannon formalised it within information theory in the late 1940s. Alec Reeves, a British engineer, patented pulse-code modulation itself in 1938 while working in France, though no contemporary equipment could implement it economically. Practical digital recording waited until the 1970s, when Sony and others built PCM processors that stored digital audio on videotape, since video recorders were the only consumer machines with enough bandwidth. That expedient is the reason for the odd 44.1 kHz figure: it is the rate that fits an integer number of samples into the active lines of both NTSC and PAL video frames. Sony and Philips codified 44.1 kHz, 16-bit stereo in the Red Book specification of 1980, and the compact disc reached the market in 1982, making a 74-minute, roughly 650 MB capacity the baseline against which all later audio storage was measured. Reducing that burden drove the next wave. A team at the Fraunhofer Institute in Erlangen led by Karlheinz Brandenburg, building on psychoacoustic masking research, developed the format standardised as MPEG-1 Audio Layer III, published in 1992, with the .mp3 file extension adopted in 1995. Advanced Audio Coding followed within MPEG-2 in 1997. Lossless alternatives appeared as storage cheapened, with Xiph.Org releasing Vorbis in 2000 and Josh Coalson releasing the Free Lossless Audio Codec in 2001, and Apple introducing ALAC in 2004. The size formulas in this calculator descend directly from those specifications.