Compress MP3 files
Lower the bitrate of MP3 music and speech, or switch to mono, right in your browser.
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How to compress MP3 files
Add your files
Drop files on the box, paste them or choose them from your device. Nothing is uploaded.
Check the settings
The default preset suits most files. Change quality, size or format if you need a smaller file.
Download the result
Save each file or all of them as one ZIP. If a file cannot get smaller, you keep the original.
MP3, the format that made music portable
MP3 (MPEG-1 Audio Layer III) was developed largely at the Fraunhofer Institute and standardized in 1993. It is lossy: it uses a model of human hearing to discard sounds you are unlikely to notice, such as quiet tones masked by louder ones at nearby frequencies. The patents expired in 2017, and MP3 remains the one audio format that every phone, car stereo, browser, smart speaker and podcast app plays.
The size of an MP3 depends only on its bitrate and duration. At 128 kbps, one minute takes 128,000 × 60 ÷ 8 = 960 KB, so roughly 1 MB per minute; at 320 kbps it is 2.4 MB per minute; a spoken-word file at 64 kbps mono needs under half a megabyte per minute.
Choosing a bitrate
| Content | Bitrate | Size per minute |
|---|---|---|
| Voice memo, lecture, audiobook | 48–64 kbps, mono | 0.36–0.48 MB |
| Podcast with music intro | 96 kbps, stereo or mono | 0.72 MB |
| Music for everyday listening | 128–192 kbps, stereo | 0.96–1.44 MB |
| Music where you want a safety margin | 256 kbps | 1.92 MB |
Mono halves the information the encoder has to describe, so for speech it lets you use a lower bitrate without the swishy, underwater sound that low-bitrate stereo produces. Lowering the sample rate from 44.1 kHz to 22.05 kHz also helps voice recordings, because speech has little energy above 10 kHz.
Constant bitrate (CBR) spends the same number of bits on every second. Variable bitrate (VBR) spends more on complex passages and less on silence, usually giving better quality for the same average size.
Making an existing MP3 smaller
Every MP3 you compress here is decoded and encoded again with LAME, the open-source MP3 encoder, running in your browser. Because MP3 is lossy, this is a second generation of loss. Going from 320 kbps to 128 kbps is usually fine for casual listening; going from 128 kbps down to 96 kbps adds audible artifacts to music faster than the numbers suggest. Two rules follow:
- Never raise the bitrate. A 128 kbps file re-encoded at 320 kbps is bigger and does not sound better; the lost detail does not come back.
- For speech, mono at 64 kbps is usually the biggest single saving; for music, try 160 kbps and listen to a passage with cymbals, which reveal artifacts first.
The output is MP3 again by default, and the format menu also offers more efficient AAC (in an M4A file) and Opus; if your browser cannot create AAC, Opus is used instead. AAC and Opus sound better than MP3 at the same low bitrate, which makes them a good choice for voice messages and podcasts if the recipient's player supports them.
Common issues
- Album art makes small files big. An embedded cover image can exceed a megabyte, more than two minutes of speech at 64 kbps.
- Cover art takes up space. Tags and cover art are kept by default, and an embedded high-resolution cover can add a megabyte to every track. Turn off "Keep tags and cover art" for files that only need to play.
- A file from a messenger sounds bad. It was already compressed hard. Compressing it again only makes it worse; go back to the original recording if you can.
MP3 questions
Is 128 kbps good enough?
For most listeners on phone speakers, earbuds and in the car, yes. On good headphones, careful listeners can hear the difference on some music; 192 kbps removes almost all doubt.
What sample rate should I use?
Keep 44.1 kHz for music. For speech, 22.05 kHz or 24 kHz is enough and lets the encoder spend its bits where they matter.
Why is my compressed MP3 the same size?
If the original already uses a low bitrate, a new encode cannot be smaller without sounding worse, so the tool keeps your file and tells you it is already optimal.
Can I compress an MP3 without losing quality?
Only marginally, by removing embedded artwork and padding with a tag editor. This tool always re-encodes, so any real reduction here means a lower bitrate, which is a lossy step.
Related tools
Uncompressed recordings are better started from the WAV page, and AAC files have their own AAC page. See all formats on the audio compressor page and read how it works.