How to Convert MP3 to FLAC — Step by Step

An MP3 file. A web browser. Understanding of what this conversion does and does not do. FLAC is a lossless format, but wrapping lossy MP3 audio in a lossless container does not restore lost quality. The FLAC file will be larger than the MP3. Do this only when you need FLAC format for a specific reason — a player that only accepts FLAC, a library that requires a single format, or a tool that only processes FLAC input.

Open the MP3 to FLAC converter on AudioUtils. Drop your MP3 file on the page. Click Convert. The tool decodes the MP3 and re-encodes the audio as FLAC. FLAC compresses the decoded audio losslessly — no additional quality loss occurs during this step. Download the FLAC file. The audio content is identical to what the MP3 contained. The FLAC container just stores it differently.

The FLAC file will be 3-5 times larger than the MP3. A 5 MB MP3 becomes 15-25 MB as FLAC. Quality stays exactly the same — you hear the same audio. The FLAC encoder preserves every sample from the decoded MP3 without any additional loss. But it cannot add back what MP3 removed. If someone asks for a "lossless version" and you only have an MP3, be honest about the source. Passing upconverted MP3 as lossless is misleading.

File is huge: Expected. FLAC files from MP3 sources are larger because FLAC stores more data per sample. Someone says the quality is bad: The quality matches the original MP3. If the MP3 was low bitrate (128 kbps or below), the FLAC will reflect that. Start from a better source if possible. Metadata differences: FLAC uses Vorbis comments, not ID3 tags. Some metadata may need to be re-entered after conversion.

FFmpeg: ffmpeg -i input.mp3 output.flac — simple and effective. Audacity: Import MP3, Export as FLAC. foobar2000: Built-in converter with FLAC encoding. dBpoweramp: Popular for batch conversion. For the best FLAC files, start from a CD or lossless source. AudioUtils handles the conversion instantly if you need FLAC format from an MP3 source.

This is the single most important thing to understand about this conversion, because it is so widely misunderstood. FLAC is a lossless format, but 'lossless' describes what it does going forward — it preserves whatever audio it is given, bit for bit — not what it can recover from the past. When MP3 was encoded, its psychoacoustic model permanently discarded audio detail it judged inaudible; that information no longer exists anywhere in the file. Wrapping that already-reduced audio in a FLAC container faithfully preserves the reduced audio, but it cannot reconstruct the detail the MP3 encoder threw away. The result is a FLAC that sounds exactly like the MP3 it came from — no better — while taking three to five times the space. There is no software, no setting, and no 'upscaling' that restores lost lossy detail; claims to the contrary are marketing, not physics. So converting MP3 to FLAC never upgrades quality. If you want genuine lossless audio, you must obtain it from a lossless source (a CD rip, a FLAC download, an uncompressed master) — not by re-wrapping an MP3.

Given that it cannot improve quality, why do it at all? There are legitimate, purely practical reasons. Player or device requirements: some high-end audio players, DACs, and streamers accept only lossless formats and reject MP3 outright, so a FLAC wrapper is the only way to play the file there. Library standardization: if you keep a single-format music library (all FLAC) for consistent tagging, ReplayGain, and player behavior, converting stray MP3s to FLAC unifies the collection — accepting that those tracks are lossless containers around lossy audio. Tool input requirements: some audio software or mastering-adjacent tools only ingest lossless input, and FLAC satisfies the parser even when the source was lossy. Editing workflows: converting to a lossless format before heavy editing prevents additional generation loss during processing (though WAV is often the better choice there). In every one of these cases you are converting for format compatibility, not quality — a valid goal, as long as you are honest that the audio inside is still MP3-grade.

Because MP3-to-FLAC produces a lossless container around lossy audio, it is exactly how 'fake FLACs' are created — and knowing how to detect them protects your library and anyone you share with. A fake FLAC is a file that carries the lossless FLAC extension and branding but whose audio originated from a lossy source like MP3, so it offers none of the quality lossless implies. The reliable way to spot one is a spectrogram (viewable in Spectro, Audacity's spectrogram view, or Spek): genuine lossless audio shows content extending up toward 20-22 kHz, while a file transcoded from MP3 shows a sharp horizontal cutoff where the MP3 encoder discarded the top frequencies — often a hard shelf around 16 kHz for a 128 kbps source, or ~19-20 kHz for higher bitrates. That cliff is the fingerprint of a lossy ancestor. The practical takeaways: never present an MP3-sourced FLAC as genuinely lossless; if you receive a 'lossless' file that matters, spectrogram-check it; and label your own conversions honestly so a future you (or a collaborator) is not misled by the extension.

The conversion is simple everywhere, and the browser needs no install. Windows: foobar2000 (free, batch-capable) or FFmpeg; Windows Media Player will not do it well. Mac: XLD or FFmpeg, since the Music app neither imports nor exports FLAC cleanly. iPhone/Android: a browser converter like AudioUtils is the easiest route, running locally with nothing to install. Command line: 'ffmpeg -i input.mp3 output.flac' is instant and scriptable for batches. Linux: FFmpeg or SoX. One useful note on FLAC compression level — it affects only file size and encode time, never quality, so any level produces identical audio; the default is fine. Whichever tool you use, the outcome is the same: the decoded MP3 audio stored losslessly in FLAC, larger than the source with matching sound. Keep the original MP3 too, since the FLAC is not a higher-quality replacement — just a different container — and there is rarely a reason to delete the smaller original.

Before converting MP3 to FLAC, check whether a different approach serves you better. If you want genuine lossless audio, do not convert the MP3 — re-source the track: rip it from CD, buy the FLAC or hi-res version, or obtain the original master. That is the only path to real lossless quality. If you only need a lossless container for editing (so that re-saving during processing adds no further loss), WAV is often the more practical choice than FLAC — it decodes instantly in every DAW and avoids FLAC's compression step, and you can convert to FLAC afterward for storage. If your goal is simply broad playback, you do not need FLAC at all — the MP3 already plays nearly everywhere, so converting up to FLAC only adds size. Reserve MP3-to-FLAC for the specific cases where a player, library standard, or tool genuinely requires the FLAC format, and reach for a lossless source, WAV, or the original MP3 in the many situations where FLAC is not actually the right answer.