MP3 Compressor
Shrink MP3 files so they fit email limits, upload faster or take less space. Pick a target bitrate, convert speech to mono for an extra saving, and check the estimated size before compressing.
- Files stay on your device
- No sign-up
- Free to use
Target bitrate
Processing happens on your device; your audio is not uploaded.
How to use MP3 Compressor
- Drop an MP3 file onto the upload area. The current bitrate and an estimate for the new size appear.
- Choose a target bitrate: 128 kbps for music, 96 for podcasts, 64 or 32 for speech.
- Tick Convert to mono for voice recordings to halve the data.
- Select Compress MP3, listen to the result and download it.
MP3 Compressor features
Size estimate first
Shows the current bitrate and how small the file will become before you compress.
Bitrates for every use
From 128 kbps music quality to 32 kbps for spoken word.
Mono option
Mixes stereo to mono, which sounds the same for speech and halves the data needed.
Tags preserved
Title, artist, album and other ID3 tags are copied to the new file.
Never larger
If the result would not be smaller, the original file is offered instead.
Private
Compression happens on your device with FFmpeg.
When to use MP3 Compressor
- Fitting a recording under an email or upload size limit.
- Reducing podcast episodes for faster downloads.
- Shrinking audiobooks and lectures for phones with limited storage.
- Compressing voice memos and interviews for archiving.
- Preparing audio for websites where page weight matters.
MP3 Compressor FAQ
How much smaller will my MP3 get?
File size is proportional to bitrate. Going from 320 kbps to 128 kbps makes a file about 60% smaller; going to 64 kbps mono makes it about 80% smaller.
Will it sound worse?
Lower bitrates remove more detail. 128 kbps is transparent for most listeners on most music; speech remains clear even at 64 kbps or lower, especially in mono.
Why was my file not compressed?
If the MP3 is already at or below the chosen bitrate, re-encoding cannot make it meaningfully smaller and would only lose quality, so the original is returned. Choose a lower bitrate.
Is re-encoding an MP3 harmful?
Each lossy encode loses a little detail. Compressing a high-bitrate MP3 once is fine; avoid repeatedly re-encoding the same file. Start from a lossless original when you can.
What about other formats?
For WAV or FLAC files, use WAV to MP3 or FLAC to MP3. To compress video soundtracks, extract the audio first.
Bitrate, quality and file size
An MP3’s bitrate is the amount of data used for each second of sound, measured in kilobits per second. Because the bitrate is constant for most MP3s, file size follows directly: one minute at 128 kbps is 128 × 60 / 8 = 960 kilobytes, roughly one megabyte. Halving the bitrate halves the file.
MP3 achieves its compression with a psychoacoustic model that discards sounds people are unlikely to hear, such as quiet tones masked by louder ones at similar frequencies. At high bitrates very little is discarded. As the bitrate drops, the encoder has to remove more, which first affects cymbals and reverb tails as swishy artefacts.
Speech is far easier to compress than music. Its frequency range is narrower and it is usually recorded with one microphone, so stereo carries no extra information. Converting to mono and using 64 kbps or less keeps voices perfectly intelligible while making files tiny, which is why podcasts and audiobooks often use such settings.
Compression works best when started from the highest-quality source available. If you have the original WAV, FLAC or high-bitrate recording, encode from that rather than from an already compressed MP3, to avoid compounding losses.