Free tool
MP3 compressor
This MP3 compressor shrinks an MP3 by writing it again at a lower bitrate: pick a setting, or the size it must fit in, and see the result’s size before you start. It offers only settings that make your file smaller.
- Free
- Only settings that shrink it
- Nothing is uploaded
Drop your MP3 file here, or Choose your MP3 file
MP3, M4A, WAV, FLAC, OGG, AAC, or the sound of an MP4, MOV or WebM video, up to 1 GB and 2 hours. Everything happens in your browser; nothing is uploaded.
MP3 encoding by LAME, open-source software.
Recording voice notes to shrink later? NoteOwl records voice notes on your Mac and transcribes them there, so what you said is searchable text, not another file to compress. Voice notes are free.
How it works
How do you compress an MP3?
Add the MP3 and the compressor reads its bitrate. Choose one of the lower settings, each with the size it will give, or switch to Target size and type the megabytes it must fit. Press Compress MP3; a smaller MP3 downloads with the original’s name and “-compressed”.
- 1
Add the MP3
Its size, length and bitrate appear at once, read from the file itself.
- 2
Choose a lower setting
Settings at or above your MP3’s bitrate are greyed out, since they would make it bigger.
- 3
Compress and compare
The result shows the size before and after, and plays on the page so you can listen first.
How does compressing an MP3 make it smaller?
By spending fewer bits on each second. An MP3’s size is its bitrate times its length, so a 128 kbps file written again at 32 kbps is about a quarter the size. At the lowest settings the compressor also makes it mono and lowers the sample rate, which suits voices.
- Smallest, 32 kbps
- Channels and sample rateMono, 22 or 24 kHz
- Ten minutes takesAbout 2.3 MB
- Small, 48 kbps
- Channels and sample rateMono, 22 or 24 kHz
- Ten minutes takesAbout 3.4 MB
- Medium, 64 kbps
- Channels and sample rateMono, the original rate
- Ten minutes takesAbout 4.6 MB
- Good, 96 kbps
- Channels and sample rateStereo kept
- Ten minutes takesAbout 6.9 MB
- High, 128 kbps
- Channels and sample rateStereo kept
- Ten minutes takesAbout 9.2 MB
| Setting | Channels and sample rate | Ten minutes takes |
|---|---|---|
| Smallest, 32 kbps | Mono, 22 or 24 kHz | About 2.3 MB |
| Small, 48 kbps | Mono, 22 or 24 kHz | About 3.4 MB |
| Medium, 64 kbps | Mono, the original rate | About 4.6 MB |
| Good, 96 kbps | Stereo kept | About 6.9 MB |
| High, 128 kbps | Stereo kept | About 9.2 MB |
Why are some settings greyed out?
Because they wouldn’t help. Writing a 128 kbps MP3 again at 128 kbps or more makes it the same size or bigger, and can’t bring back detail the first encoding dropped. The compressor reads your file’s bitrate and offers only the settings below it.
Does compressing an MP3 lose quality?
Yes, some: the sound is decoded and encoded again with less room, so the finest detail goes first. Speech holds up well, which is why the speech settings are mono. Music is best kept at 96 kbps or more. Keep the original MP3 if you might want it later.
A 6:44 podcast at 128 kbps became a 1.54 MB file at 32 kbps mono, 75% smaller. A 320 kbps song asked to fit in 5 MB was written at 224 kbps, still stereo, at 4.81 MB.
How do you make an MP3 a certain size?
Choose Target size and type the limit in megabytes, or press 25, 10 or 5 MB. The compressor picks the highest bitrate whose file still fits, with a little to spare, and shows it before you start. If nothing fits, it tells you the smallest size it can make.
25 MB
Gmail’s limit for attachments. About an hour of speech fits at 48 kbps.
10 MB
Upload forms and some message apps. Ten minutes of music fits at 128 kbps.
5 MB
Tight limits. Twenty minutes of speech fits at 32 kbps.
How do you keep voice notes without piling up MP3s?
Keep them as text. NoteOwl records voice notes on your Mac and transcribes them there, so each one is words you can search and copy rather than a file to compress. Voice notes and dictation into any app are free in NoteOwl.
FAQ
Questions about compressing MP3 files
Is my MP3 uploaded to be compressed?
No. The MP3 compressor runs in your browser tab: it reads the file from your device, writes the smaller MP3 in the page and hands it back as a download. Compressing a 6.2 MB podcast sent nothing over the network.
What bitrate should I compress an MP3 to?
For speech, 48 or 64 kbps mono: voices stay easy to follow at a fraction of the size. For music, 96 or 128 kbps keeps stereo and most of the detail. The lowest setting, 32 kbps mono, is for when size matters most.
Why did my compressed MP3 become mono?
The three speech settings, 32 to 64 kbps, keep one channel so every bit goes to the voices; both sides of a stereo recording are mixed into it. Choose Good or High to keep both channels of a song.
How long does compressing take?
A few seconds for most MP3s. A 6:44 podcast took about three and a half seconds in Safari’s engine; longer files take time in proportion to their length.
Can I compress several MP3s at once?
One at a time on this page. To make one smaller file from several MP3s, join them first with NoteOwl’s MP3 joiner, then compress the result here.
Can I compress other formats here?
The page is set up for MP3s, but it opens other audio too. For WAV, M4A or video sound, NoteOwl’s audio compressor does the same job, and the WAV compressor can also make a lossless FLAC.
Keep exploring
More audio editing tools
- WAV compressorMake a WAV smaller in your browser: lossless FLAC, a smaller WAV (lower sample rate, mono, 16-bit) or MP3, with the size before and after
- Volume boosterMake an audio file louder in your browser, up to +30 dB, with a limiter that stops it clipping and a preview before you save
- Audio speed changerSpeed up or slow down an audio file from 0.5× to 2× in your browser, keeping the pitch or not, and save it as MP3 or WAV
- Audio trimmerTrim the start and end off a recording in your browser by dragging on its waveform; MP3, M4A, WAV and FLAC are cut without re-encoding
Related
- M4A to MP3 converterConvert M4A to MP3 in your browser, iPhone and Mac voice memos included, at 128, 192 or 320 kbps; nothing is uploaded
- Online voice recorderRecord your voice in the browser with a level meter, timer and pause, play it back, and save it as MP3 or WAV; nothing is uploaded
- Voice notes on your MacVoice notes and dictations saved as searchable text on your Mac, with the raw words beside the polished version; free
Voice notes as searchable text, on your Mac
Free to download. Runs entirely on your Mac.
macOS 26 or later · Apple Silicon (M1 or newer) · 16 GB memory minimum, 24 GB recommended
About NoteOwl
NoteOwl is private AI meeting notes and memory for the Mac. It captures meetings without a bot joining the call, labels every speaker, writes summaries and action items, and builds a memory of every conversation that you can chat with — fully offline, because the speech recognition and the AI run on the Mac itself. Dictation into any app is free; Pro is a one-time purchase.
NoteOwl pricing: what’s free and what Pro adds
Last updated