How is audio file size calculated from bit rate?

File size (bytes) = (Bit rate in bps × Duration in seconds) ÷ 8. For example, a 3-minute track at 320 kbps = (320,000 × 180) ÷ 8 = 7,200,000 bytes ≈ 7.2 MB. This is a theoretical value; actual files may be slightly larger due to metadata headers.

Is 128 kbps good enough for music?

For casual listening on earbuds or laptop speakers, 128 kbps MP3 is adequate. Critical listeners and audiophiles will notice compression artifacts — especially in high-frequency content like cymbals and strings. For serious listening, 256 kbps AAC or 320 kbps MP3 is recommended.

What is the difference between 320 kbps MP3 and lossless?

A 320 kbps MP3 discards audio data the encoder considers inaudible using psychoacoustic models. A lossless file (FLAC or WAV) retains every sample from the original recording. Lossless files are typically 5–10 times larger than 320 kbps MP3 for the same track.

Which format should I use for podcasts?

For speech-only podcasts, 128 kbps mono MP3 or 96 kbps mono AAC is the industry standard — it sounds clear for voice and keeps file sizes small for download. For music-heavy shows, 192 kbps stereo is a good balance.

Does a higher bit rate always mean better sound?

Up to the source quality ceiling, yes. Encoding a 128 kbps MP3 at 320 kbps will not recover lost detail — the output will just be a larger file. Always start from the highest quality source available.

What bit rate does Spotify use?

Spotify streams at 24 kbps (Low), 96 kbps (Normal), 160 kbps (High), and 320 kbps (Very High, Premium only) for Ogg Vorbis. Spotify HiFi (lossless) is also rolling out. Apple Music streams AAC at up to 256 kbps, plus lossless ALAC at CD quality and above.

Audio Bit Rate & Quality Guide

Enter a bit rate and duration to calculate file size, then compare MP3 128 kbps, 320 kbps, AAC, and lossless side by side to choose the right format.

Bit Rate & Duration

Bit Rate (kbps)

Duration

min

sec

Default: 3 min 30 sec — a typical pop song.

Channels

Mono audio at a given kbps has roughly twice the effective quality per channel versus stereo.

File Size

—

Total Bits

—

Mbit

Duration

—

seconds

Enter values above to see quality rating.

Format Comparison

At current duration — click a row to apply that bit rate

Format	Bit Rate	File Size	Quality

Size vs. Lossless —

0% 25% 50% 75% 100% (lossless)

Applied!

Summary

Enter a bit rate and duration to calculate file size, then compare MP3 128 kbps, 320 kbps, AAC, and lossless side by side to choose the right format.

How it works

Enter the audio bit rate in kbps (e.g. 128, 256, 320) or select a preset from the dropdown.
Enter the track or recording duration in minutes and seconds.
The tool multiplies bit rate by duration to get total bits, then divides by 8 to convert to bytes and displays the result in KB, MB, or GB.
The quality comparison table recalculates file size for every standard format at your chosen duration so you can compare them directly.
A quality rating for each format explains the trade-off between file size, audible detail, and typical use case.

Use cases

Estimate how much storage a music library will consume at different quality settings.
Decide between streaming tiers (e.g. Spotify Normal vs. High vs. Very High) based on data usage.
Choose the right export format when publishing a podcast or audiobook.
Compare lossless vs. lossy file sizes before ripping a CD collection.
Plan storage for a DJ set or live recording at a specific bit rate.
Verify that an audio file size on disk matches its stated bit rate and length.

Frequently Asked Questions

Last updated: 2026-09-22 · Reviewed by Nham Vu