Audio File Size Calculator

Audio file size for uncompressed audio comes from four things: sample rate, bit depth, channel count, and duration. Nothing else. There is no compression to guess at, so the number is exact rather than an estimate.

Uncompressed audio (WAV/AIFF) formula: File Size (bytes) = Sample Rate × Bit Depth × Channels × Duration (seconds) ÷ 8

The ÷ 8 is the step people skip. Everything before it is in bits, and file sizes are quoted in bytes. Forget it and you overstate the file by a factor of eight.

A note on MB. This page uses decimal megabytes, where 1 MB = 1,000,000 bytes, because that is the convention bit rates and drive capacities use. Windows divides by 1,048,576 instead and calls that MB too, so it will report a number about 4.6% smaller for the same file. Neither is wrong; they are different units wearing the same label.

Where:

• Sample Rate = samples per second (Hz). Common: 44,100 Hz (CD quality), 48,000 Hz (video), 96,000 Hz (studio)
• Bit Depth = bits per sample. Common: 16-bit (CD), 24-bit (professional), 32-bit float (editing)
• Channels = 1 (mono), 2 (stereo), 6 (5.1 surround)
• Duration = length in seconds

Compressed audio (MP3/AAC) formula: File Size (bytes) = Bit Rate (bps) × Duration (seconds) ÷ 8

Common MP3 bit rates and quality:

Uncompressed reference:

• CD quality (44.1 kHz, 16-bit, stereo): 10.6 MB per minute, a data rate of 1,411 kbps
• Studio quality (96 kHz, 24-bit, stereo): 34.6 MB per minute, or 4,608 kbps

Worked example

A 4-minute song at CD quality WAV. Four minutes is 240 seconds:

Size = 44,100 × 16 × 2 × 240 = 338,688,000 bits 338,688,000 ÷ 8 = 42,336,000 bytes = ~42.3 MB

Note what the intermediate number is. 338,688,000 is the bit count, and quoting it as bytes is the single most common mistake on this calculation. A four-minute CD track is not a 338 MB file. If it were, an audio CD would hold about four songs.

Same song as a 320 kbps MP3:

Size = 320,000 × 240 ÷ 8 = 9,600,000 bytes = ~9.6 MB

Compression ratio: 42.3 / 9.6 = 4.4 to 1. That falls straight out of the bit rates, 1,411 kbps against 320 kbps, and it is the honest figure. MP3 at 320 kbps is roughly a quarter the size of the WAV, not a thirtieth. The dramatic ratios people quote usually compare against 128 kbps, where WAV is 11 times larger.

Streaming data usage: an hour of Spotify at 320 kbps is ~144 MB. Apple Music Lossless (ALAC at 1,411 kbps) is ~635 MB an hour, which is the same data rate as the CD it came from, because that is exactly what lossless means.