In this guide
FLAC compresses supported PCM audio losslessly; MP3 uses lossy compression to reduce data. Keep a trustworthy lossless source for archiving or future work, and create an MP3 copy when its size or compatibility is useful. Converting an MP3 to FLAC cannot restore discarded audio information.
FLAC preserves the encoded audio samples losslessly; MP3 uses lossy compression to create smaller files. Choose FLAC when you need a sample-preserving copy of a suitable source, and MP3 when smaller files or compatibility matter more than keeping every encoded sample.
Neither extension guarantees a recording’s history. A FLAC made from an earlier MP3 preserves the already-decoded MP3 audio; it does not reconstruct information the earlier lossy encoding discarded. Likewise, a higher-bitrate MP3 made from a low-bitrate file does not restore the original source.
FLAC vs. MP3 at a glance
| Question | FLAC | MP3 |
|---|---|---|
| Compression | Lossless for supported PCM input: decoding reconstructs the encoded samples. | Lossy: the encoder discards information to reduce data. |
| File size | Varies with source, duration and settings; often larger than an MP3 of the same recording. | Depends on bitrate, duration and metadata; a constant-bitrate file is roughly predictable. |
| Best use | Preserving a suitable source and making future copies without another lossy encoding. | Portable listening and delivery where a smaller, compatible file is useful. |
| Playback | Supported by many apps and devices, but check the actual destination. | Widely supported, although features and metadata behavior can still differ. |
| Repeated exports | A lossless encode can preserve the PCM supplied to it; editing or changing sample format may still alter audio. | Each new lossy encode can introduce further changes; return to the best source. |
RFC 9639 specifies FLAC as a lossless audio codec. Its lossless property describes the relationship between the encoded PCM input and decoded samples, not whether the recording was clean or previously lossless.
Can you hear the difference?
Sometimes, but not always. Audibility depends on the source, MP3 encoder and bitrate, playback chain, listening conditions and listener. A high-bitrate MP3 may sound indistinguishable from a lossless source in a particular test, while a difficult passage or lower-bitrate encode may reveal artifacts. File size or bitrate alone does not prove that one listener will hear a difference.
For a useful comparison, create both versions from the same trustworthy master, level-match them, and compare the same passage without knowing which version is playing. Check difficult moments such as cymbal tails or dense transients, but avoid declaring a universal threshold from one test. Different masters or loudness levels can make a comparison misleading.
How much space do they use?
For a constant-bitrate MP3, a rough audio-data estimate is bitrate × duration ÷ 8. A four-minute file at 320 kilobits per second is about 9.6 MB of encoded audio; at 128 kilobits per second it is about 3.84 MB. These use decimal MB and exclude tags, artwork and other overhead. Variable-bitrate files depend on their actual average bitrate.
FLAC does not have one fixed size for a given duration. Its result depends on how compressible the source is as well as its sample format and encoder settings. Different lossless compression levels can produce different file sizes while preserving the same supported input samples; see the FLAC project’s FAQ.
Use the audio file size calculator for a bitrate-and-duration estimate. A FLAC estimate based on an assumed bitrate is only a planning estimate, not a guarantee of the encoded size.
Which format should you choose?
- Keep or archive a master: Preserve an original lossless source when available. FLAC can reduce storage compared with equivalent uncompressed PCM while preserving supported samples. Keep backups and retain the original metadata where it matters.
- Edit or produce music: Start from the best available source and check the editor’s supported formats. An editor may decode FLAC to PCM internally; preserve the project, source media and suitable working exports.
- Send a small listening copy: MP3 is often convenient. Agree on a format and bitrate with the recipient, then listen to the actual file and confirm it plays in the destination.
- Compare a music library: Consider storage, player support and where the files came from. A large FLAC is not proof that its source was lossless, and converting a lossy file does not improve its history.
How to convert FLAC to MP3
- Keep the original FLAC. Work from an authorized file and save the MP3 as a separate copy.
- Open a supported file. The FLAC-to-MP3 converter accepts a compatible local FLAC up to five minutes and 50 MiB, subject to browser decoding support. Decoded audio must be mono or stereo.
- Choose a bitrate. The tool offers 128, 192 and 320 kbps. Higher bitrate usually uses more space, but quality depends on the source and encoder as well.
- Convert and listen. Preview the actual MP3, check the start, end and a busy passage, then download it. The output must also fit the tool’s size limit.
- Check the destination. Confirm playback and metadata in the app or device you plan to use. See the conversion guide for browser and desktop options.
MP3 encoding can add delay or padding; the output duration or alignment can differ slightly. If precise synchronization matters, check the actual export in the timeline and retain the source.
Can MP3 be converted back to FLAC?
Yes, a compatible converter can decode an MP3 and encode those decoded samples as FLAC. The result can be lossless with respect to that decoded MP3, but it cannot recover detail removed by the earlier MP3 encode. It may also be much larger. If you need the original lossless recording, obtain it from a suitable source instead.
Common questions
Is FLAC always better quality than MP3?
FLAC preserves its encoded PCM input, while MP3 does not. Audible quality depends on the source, mastering, encoding and listening conditions; a FLAC made from a poor or lossy source is not automatically a better-sounding recording.
Is 320 kbps MP3 lossless?
No. It is a relatively high MP3 bitrate, but MP3 remains a lossy codec. The result can sound very close to the source in some listening conditions without being sample-identical.
Can I convert FLAC to MP3 without losing quality?
The MP3 encode is lossy, though its changes may or may not be audible in a particular comparison. Keep the FLAC if you need the original encoded samples.