Audio Compressor (Reduce Audio File Size)
Make audio files smaller in your browser: choose a bitrate or a target size in MB, mono for speech, MP3, Opus or M4A. Batch files, nothing uploaded.
Shrink audio files to fit an email, a messenger or an upload limit. Pick a lower bitrate, switch speech to mono, or simply type the size you need in MB and let the tool work out the bitrate from the length. MP3 is encoded right in your browser; Opus and M4A use the built-in ffmpeg engine. Your files are never uploaded.
How to use this tool
- Choose one or more audio files.
- Pick the format: MP3 for compatibility, Opus for the smallest speech files, M4A for Apple devices.
- Choose a bitrate (64 kbps mono is plenty for voice), or enter a target size in MB.
- Press Calculate and compare the sizes in the results.
Formula
Bitrate for a target (kbps) = target bytes × 8 ÷ 1000 ÷ seconds × 0.97 · Size ≈ kbps × 1000 ÷ 8 × seconds
The 3% margin covers headers and frame padding. MP3 bitrates come in fixed steps, so the next step down is used, and the sample rate is lowered to suit the bitrate the way the LAME encoder recommends (for example 22.05 kHz for 64 kbps stereo, 24 kHz for 40 kbps mono), never above the original. If a file would not get smaller, the original is offered unchanged.
Example
A 25-minute talk must fit a 10 MB limit: 10,000,000 × 8 ÷ 1000 ÷ 1,500 × 0.97 ≈ 51.7 kbps, so MP3 uses 48 kbps (mono, 32 kHz) and the file comes out at about 48,000 ÷ 8 × 1,500 = 9.0 MB.
Frequently asked questions
Which bitrate is good enough?
Speech: 48–64 kbps mono in MP3, or 24–32 kbps in Opus. Music: 128 kbps is acceptable, 160–192 kbps sounds close to the original.
Why did the file not get smaller?
If the original already uses a lower bitrate than the one chosen, re-encoding cannot shrink it, so the original is kept. Choose a lower bitrate or mono.
Does compressing reduce quality?
Yes, every lossy encode removes some detail, and lower bitrates remove more. Keep the original if you may need full quality later.
Last updated:
Page address with these inputs: https://kakao.mobile/tools/audio-compressor/
Cite or embed this tool
kakaoCalc. (2026, November 8). Audio Compressor (Reduce Audio File Size). https://kakao.mobile/tools/audio-compressor/
“Audio Compressor (Reduce Audio File Size).” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/audio-compressor/.