Compress MP3

Reduce MP3 file size, then check the actual saving

Compress MP3 audio when a recording is too large to share or store comfortably. This tool re-encodes your original at a selected constant bitrate, starting at 128 kbps. It shows the size of the input beside the completed output, including how much smaller or larger the result is. The comparison uses actual file bytes, not a promised compression percentage.

How to compress an MP3

1. Choose one MP3 file, up to 30 MiB and ten minutes. You can also try the music sample to see the workflow.
2. Pick a bitrate below the source's approximate bitrate. The available presets are 128, 192, 256 and 320 kbps.
3. Check the estimated output size. This is the encoded audio payload; the final file also contains headers and tags.
4. Create the audio and compare the actual original and output sizes. Listen to both versions, especially detailed or quiet passages.
5. Download the MP3 if the result meets your needs. Save it before leaving or refreshing this page.

Understand smaller, larger and unchanged results

The result panel calculates the change as the difference in bytes divided by the original file size. A positive saving is labelled smaller; an increase is labelled larger. Sizes use MiB, where one MiB is 1,048,576 bytes. Many upload services use decimal MB instead, so check the recipient's exact byte limit if your file is close to it.

A lower bitrate usually means fewer encoded audio bytes for the same duration. For example, moving from 320 to 128 kbps reduces the audio payload by roughly 60%. That is a mathematical example, not a guaranteed saving for your file: metadata, duration framing and the original encoding affect the final result.

Already-small inputs may not shrink. A 64 or 96 kbps recording cannot be made smaller by choosing this tool's minimum 128 kbps preset. A VBR file may also have an average bitrate below the selected setting. The estimate warns when the payload alone is at least as large as the original; after export, the actual comparison is the final check.

Choose size savings without losing more than you need

MP3 compression is lossy. Re-encoding can discard additional detail, even if the new file uses the same bitrate. Keep your original and compare a few settings from that original instead of compressing an already-compressed result again. Listen for changes in cymbals, consonants and reverb tails; a smaller file is useful only if it still works for its intended purpose.

If you need a particular delivery bitrate rather than a smaller attachment, use the MP3 bitrate converter. For planning around a file limit, follow the guide to reducing MP3 file size. If your source is an uncompressed recording, start with WAV to MP3.