Compress MP3 online
MP3 size scales linearly with bitrate, which means the result of compressing one can be worked out in advance — to within a couple of percent.
Select the files you want to compress or convert and upload them here.
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Supported compression and conversion formats:
JPEG, JPG, PNG, GIF, WEBP, MP3, TIFF, TIF, BMP, DIB, RLE, JP2, JPF, JPG2, JPX, J2K, JPC, MJ2, OGG, OGV, SPX, WAV, 3GP, AAC, M4A, M4B, OPUS, OGA, MP4, AVI, MKV, MKA, SVG, EXR, RAW, ARW, SRF, SR2, CRW, CR2, CR3, DNG, DCR, KDC, ERF, 3FR, MEF, MRW, NEF, NRW, ORF, PEF, RAF, RWL, RW2, SRW, X3F, PDF, JXL.
What compressing an MP3 actually does
An MP3 does not store sound but a model of it: the encoder has already discarded everything it calculated your ear would not miss. How much is left is set by the bitrate — kilobits per second. Re-compressing decodes the file and encodes it again, this time with a smaller allowance.
That gives simple arithmetic: 320 kbps is 2.4 MB per minute, 192 is 1.4 MB, 128 is 0.96 MB, 64 is 0.48 MB. Multiply by duration and you have the size of the result. Nothing goes below 32 kbps here — speech starts to smear past that point.
Which bitrate to pick
There is no universal answer, only what is in the file.
Honest about the losses
Every re-compression is a second generation of loss: the encoder lays its own artefacts over someone else's. Taking 320 kbps down to 128 once is fine and few people hear it. Re-encoding a file that was already 128 kbps down to 128 again is a bad idea — even what survived the first pass suffers.
So the rule is simple: compress from the best original you have, straight to the value you need. Intermediate steps only cost you sound.
| Bitrate | Per minute | Per hour | Good for |
|---|---|---|---|
| 320 kbps | 2.4 MB | 137 MB | music, no compromises |
| 192 kbps | 1.4 MB | 82 MB | music, difference barely audible |
| 128 kbps | 0.96 MB | 55 MB | background, car, messengers |
| 64 kbps, mono | 0.48 MB | 27 MB | lecture, interview, podcast |
| 32 kbps, mono | 0.24 MB | 14 MB | voice memo, audiobook |
Common questions
How do I compress an MP3 to 8 MB?
Divide 8 MB by the length of the recording. A four-minute track fits into 8 MB at 256 kbps, where quality barely suffers. An hour-long lecture would need 18 kbps, which is below anything reasonable — convert it to mono and split it into parts instead.
How do I compress an MP3 without losing quality?
You cannot: MP3 is a lossy format and every re-encode takes something. If the file must shrink while staying bit-for-bit identical, the only honest option is a ZIP archive — and on MP3 that gains a few percent at most.
Will compression shorten the track?
No. Duration, tags, cover art and track order all stay — only the amount of data per second of sound changes.
Why did my file barely get smaller?
It was most likely already compressed harder than the quality you picked. Re-encoding upward adds no quality and no size, so the file is left alone rather than damaged for nothing.