Calculating sound file size

5 minAS Level1.2.7

AI-drafted, independently checked · not yet teacher-reviewed

By the end of this lesson

By the end you can calculate the size of an uncompressed sound file, and predict how changing the sampling rate, the sampling resolution or the length changes it.

The bitmap formula, wearing headphones

A sound file is a long list of samples. Count the samples, multiply by the bits in each one, and that's the file size.

If you can do bitmap file sizes, you can already do this. Only the names change.

The formula

$\text{file size (bits)} = \text{sampling rate (Hz)} \times \text{sampling resolution (bits)} \times \text{length (s)}$

Sampling rate × length = the number of samples.
× sampling resolution = the number of bits.
÷ 8 for bytes, then ÷ 1024 for KiB, and ÷ 1024 again for MiB.
Recorded in stereo? There are two channels (left and right), so multiply by 2.

Worked example: A voice memo

A voice memo lasts 10 seconds. It is recorded in mono with a sampling rate of 8 kHz and a sampling resolution of 8 bits. Calculate its size in bytes.

Have a go first?

Quick check

CalculateQuestion 1 · Apply

A 30-second mono recording uses a sampling rate of 16 000 Hz and a sampling resolution of 8 bits. Calculate its file size in bytes.

bytes

Answer the question above to continue.

Previous lessonSampling rate, sampling resolution and accuracy Next lessonWhy compress? Smaller files, faster everything

A toy recording at 8 Hz so every bit fits on screen. Real audio has thousands of columns per second.