Hong Life CalculatorsUnderstanding the audio file size calculator — concept and principle
How much storage does a recording need? For uncompressed audio such as WAV or AIFF, size depends on sample rate, bit depth and number of channels; for compressed formats such as MP3, AAC or Opus, it depends on the bitrate. This calculator gives the file size in MB, MiB and GB, the data rate, size per minute and how many minutes fit in 1 GB.
How it is calculated
PCM data rate (bit/s) = sample rate × bit depth × channels
Compressed data rate = bitrate (kbps) × 1,000
File size (bytes) = data rate × duration (s) ÷ 8
MB = bytes ÷ 1,000,000; MiB = bytes ÷ 1,048,576; GB = bytes ÷ 10⁹
Minutes per GB = 10⁹ ÷ (data rate × 60 ÷ 8)
The principle
Digital audio records the sound wave's level many thousands of times per second. Each measurement (sample) uses a fixed number of bits, and stereo stores two channels. Multiplying these gives bits per second; dividing by 8 converts to bytes. Compressed formats discard information the ear is unlikely to notice and are described directly by their average bitrate. Note the two meanings of "megabyte": storage makers use 1,000,000 bytes, while some operating systems display 1,048,576 bytes (a mebibyte) as "MB".
Worked example
Default inputs: uncompressed PCM, 4 minutes, 44.1 kHz, 16-bit, 2 channels.
- Data rate = 44,100 × 16 × 2 = 1,411,200 bit/s = 1,411.2 kbps (CD audio).
- Duration = 4 × 60 = 240 s.
- Size = 1,411,200 × 240 ÷ 8 = 42,336,000 bytes = 42.3 MB = 40.4 MiB = 0.042 GB.
- Size per minute = 1,411,200 × 60 ÷ 8 = 10.58 MB.
- Minutes in 1 GB = 1,000,000,000 ÷ 10,584,000 = 94.
| Length of the recording (minutes) | File size (MB) |
|---|---|
| 1 | 10.6 |
| 2 | 21.2 |
| 3 | 31.8 |
| 4 | 42.3 |
| 5 | 52.9 |
| 6 | 63.5 |
| 8 | 84.7 |
How to read the result
CD-quality WAV uses about 10.6 MB per minute, while a 320 kbps MP3 uses about 2.4 MB per minute, a little under a quarter. 24-bit, 96 kHz studio recordings use more than three times the CD rate. Streaming services offer several bitrates; Spotify, for example, lists 24 to 320 kbps. Variable-bitrate files vary around their average, so real sizes differ slightly.
Common mistakes
- Confusing kilobits (kbps) with kilobytes.
- Mixing MB and MiB when comparing with a computer's display.
- Forgetting the number of channels; stereo doubles PCM size.
- Expecting compressed bitrate to change with sample rate; it is set directly.
Frequently asked questions
How big is a 3-minute song as WAV?
At CD quality about 31.8 MB.
Why does my computer show a smaller number?
It may count in MiB (1,048,576 bytes) while labelling them MB.
Is higher bit depth always better?
It gives more dynamic range, useful for recording and editing; for playback 16-bit is often sufficient.
What does 320 kbps mean?
320,000 bits of audio data per second.
Sources: Library of Congress, Sustainability of Digital Formats, "Linear Pulse Code Modulated Audio (LPCM)" and "WAVE Audio File Format" · Spotify Support, "Audio quality" · IEC 80000-13 (binary prefixes such as MiB)