Compress MP3 files in your browser
Pick a bitrate, or a size to land under. Speech in mono at 64 kbps is a fraction of the original and sounds the same on a phone.
or browse your device. Everything is processed on this device
How to compress an MP3
It is decoded in this tab. There is no upload endpoint, and no limit on how long the recording is.
128 kbps suits music, 96 or 64 with mono turned on suits anything that is people talking.
Duration, bitrate, channels and sample rate are shown for the file you get back, along with the size of any cover art that was thrown away.
A plain MP3 that plays anywhere, written straight from memory to your downloads.
What actually makes an MP3 smaller
MP3 is lossy. The encoder throws audio away on the way in and cannot put it back, so re-encoding an MP3 loses a second helping on top of the first. Where you still have the original recording, the WAV, the interview file, the export from your editor, encode once from that rather than squeezing a file that has already been squeezed. Where you do not, this page is the honest second best.
There are only three levers worth pulling. Bitrate is the big one, and it is a straight trade: 128 kbps is half the size of 256 and most people will not hear the difference on a laptop speaker or in a car. Mono is the second, and on speech it is close to free: two channels of one person talking into one microphone carry the same content twice, so downmixing halves the file and changes nothing you would notice. Cover art is the third and the easiest, because a 400KB album photo inside a 3MB podcast episode is more than a tenth of the file doing no work at all.
What does not work is asking for the same audio at a lower bitrate with no loss. There is no setting for that, here or anywhere. Anyone offering it is either stripping tags, which we do too, or lying.
If the file only ever has to play in a browser or a modern app, MP3 is not the format to choose. Opus is dramatically better at the same bitrate: 64 kbps Opus is roughly the quality of 128 kbps MP3 on speech, and it keeps working down at 24 kbps where MP3 falls apart. AAC sits between the two and is what Apple has shipped for twenty years. MP3 survives for one reason, which is that absolutely everything on earth plays it, from a car stereo of 2004 to a hospital dictation system. That compatibility is the whole argument for it. If you need it, stay here. If you do not, encode as Opus instead and use half the bytes.
Video is a different job and belongs at vidshift.io, which does it properly in the browser. Dropping an MP4 here will not work, and extracting the soundtrack is a conversion rather than a compression.
MP3 compression FAQ
How do I make an MP3 smaller for email?
Most mail providers stop at 20 to 25MB. Turn on "Compress to a target size", type 10000 for 10MB, and you will clear every common limit. For a spoken word recording, turning on mono and choosing 64 kbps usually gets you under that without setting a target at all: an hour of speech at 64 kbps mono is about 28MB, and at 32 kbps it is 14MB.
Does compressing an MP3 lose quality?
Yes, always, and twice over, because the file was already lossy before you got here. What that sounds like depends on how far you go. Dropping 256 kbps music to 192 or 160 is inaudible to nearly everyone. At 128 cymbals and applause start to sound slightly glassy. At 96 stereo music gets a watery, swirling quality in the high end, and below 64 it is obvious to anyone. Speech is far more forgiving: voice at 64 kbps mono is perfectly clear, and most podcasts you listen to are encoded at exactly that.
What bitrate should I use for a podcast?
64 to 96 kbps, mono. That is what the professional podcast networks ship, and it is roughly 30MB an hour. Stereo buys you nothing when the recording is one or two people talking into microphones, so mono is the setting to reach for first: it halves the file before you have touched the bitrate at all. Save 128 kbps and stereo for episodes with music in them.
Can I compress an MP3 without losing quality?
Not the audio itself. Any change to the bitrate means re-encoding, and re-encoding an MP3 always discards a little more. What is free is everything wrapped around the audio: turn on "Strip tags and cover art" and leave the bitrate where it is, and you get the album artwork and the ID3 frames back as usable space with the sound untouched. On a file with a large embedded cover that alone can be 10 to 20% of it.
Why is my MP3 so big?
Three usual reasons. It is long, and length multiplies everything. It is at a high bitrate, often 256 or 320 kbps, because it was ripped or exported on a setting nobody revisited. Or it is stereo when the content is one person talking, which doubles the file for no benefit. The result panel here tells you the duration, the bitrate it was, and the channel count, so you can see which of the three you are dealing with before you change anything.
How do I compress an MP3 to a specific size?
Audio is the one format where this is arithmetic rather than a search. A constant bitrate file is bitrate multiplied by duration, so we read the length of your recording and work out the bitrate that fits your figure, then round down to one MP3 actually supports. If your target needs less than 32 kbps, which is where MP3 stops, we tell you the smallest size the file can reach rather than handing back something four times over budget.
Should I use Opus or AAC instead?
On quality alone, yes. Opus at 64 kbps is about the quality of MP3 at 128 for speech, and it stays usable at bitrates where MP3 is unlistenable. AAC is comfortably better than MP3 too. MP3 wins on one axis only, compatibility, and it wins that one absolutely: every car stereo, every cheap player, every piece of ageing software reads it. If the file has to work everywhere, stay with MP3. If it only has to play in a browser or a phone app, Opus will do the same job in half the bytes.
Can I compress the audio in a video file here?
No. This page reads MP3s. Video belongs at vidshift.io, which compresses it in your browser under the same rules as this site: nothing uploaded, nothing stored.
Are there length or size limits?
None that we impose. A three hour recording is fine; the ceiling is your own device memory. The encoding runs in a worker, so the page stays responsive while a long file is working.
Does my audio get uploaded?
No. The decoder and the LAME encoder both run in this tab as WebAssembly. Open your network tab and watch: the page downloads the encoder once, and your file never becomes a request.
Other compressors
Same format joins the queue. Anything else re-routes to its own tool.