What lossless actually means
The FLAC vs MP3 question usually gets asked backwards. People want to know which format sounds better, when the more useful question is what each one keeps and what each one throws away.
Start with the raw material. CD-quality audio stored as WAV or AIFF is uncompressed PCM: every sample intact, at roughly 10 MB per minute. (WAV and AIFF hold the same audio in different containers; WAV came out of the Windows world, AIFF out of Apple's.) FLAC takes that same audio and compresses it the way a zip file compresses a document. The file lands at about 50 to 60 percent of WAV size, and on playback the decoder reconstructs the original samples exactly, bit for bit. That is what lossless means. Nothing is approximated, nothing is gone.
MP3 works differently. It is lossy compression: it permanently discards the parts of the audio the encoder judges you are least likely to hear. The payoff is a much smaller file that plays on essentially everything ever made. The cost is that the discarded data is gone for good. No setting, no software, and no future converter brings it back.
Can you actually hear the difference?
Here is the part most format guides dance around. At 320 kbps, MP3 is near-transparent for most listeners, and on normal gear most people cannot reliably tell a 320 kbps MP3 from the FLAC it came from. If that describes you, nothing is wrong with your ears or your speakers. It means the encoder is doing its job.
Bitrate matters a great deal, though. At 128 kbps the compromises become audible on good playback gear, and the gap between 128 and 320 is far larger than the gap between 320 and lossless. We dig into where the practical sweet spot sits in our guide to the best MP3 bitrate for music.
The only test that matters is your own. Take a lossless file you know well, encode a 320 kbps copy, and switch between them on the gear you actually use. If you cannot hear a difference, believe your ears over the spec sheet.
So if 320 kbps sounds the same, why bother with FLAC at all? Because sounding the same today and being the same are different things, and the difference shows up the moment you do anything with a file besides press play.
Why FLAC still wins for archiving
An archive is not a listening copy. It is the version every future copy gets made from, and that changes the math completely.
A FLAC file can become anything. Need an MP3 for an old car stereo? Encode one from the FLAC and it is a clean first-generation copy. Need M4A for an Apple device, or whatever format matters in ten years? Same story. A lossless master never boxes you in.
An MP3 archive is a dead end by comparison. Every lossy-to-lossy conversion adds a small generation loss, so an MP3 re-encoded to another lossy format comes out a little worse than either encode alone. Repeat that across years of devices and format migrations and the damage stacks up. Meanwhile, whatever the MP3 discarded on day one stays gone.
FLAC also earns its keep on plain practicality. At roughly half the size of WAV it stores identical audio for far less disk space, and it carries rich tags, so artist, album, and artwork travel with the file, something plain WAV was never good at.
What actually happens when you convert
FLAC to MP3 is the everyday direction. Keep the FLAC as your master, then encode MP3s for the places lossless is overkill: a phone with limited storage, an ancient player, a quick file for a bandmate. Convert at 320 kbps and the file gets far smaller while giving up almost nothing you can hear. Our FLAC to MP3 converter does exactly this.
MP3 to FLAC is the direction people get wrong. Converting lossy to lossless never restores lost quality. The FLAC will preserve every flaw of the source MP3, faithfully, in a bigger file. There is one honest reason to do it anyway: freezing. If a track is about to go through editing or more processing, converting it to lossless first means the rest of the chain adds no further generation loss on top of the original encode. Our MP3 to FLAC converter handles it, just go in knowing what it can and cannot do.
A sensible setup for most people
Keep lossless masters of anything you cannot re-download or re-record: your own mixes, bounces, session exports, one-of-a-kind recordings. FLAC is the right home for those. Then make 320 kbps MP3s for daily listening and sharing, and treat them as disposable, because the master can regenerate them any time.
And if a song only exists as an MP3, keep the MP3. Do not upgrade it to FLAC hoping for better sound. The original file is already the best version you have.
Convert either way, free, in your browser
We built a free Audio Converter for exactly this housekeeping. It uses FFmpeg compiled to WebAssembly to convert between MP3, WAV, M4A, FLAC, OGG, and AIFF, with a bitrate picker from 128 to 320 kbps. It runs in the browser, nothing uploaded, we never see the file. Drop in a FLAC, pick MP3 at 320, and your listening copy is ready in moments.
That covers the format side. When a project grows past conversion into stems, vocals, and mastering, that is what our desktop app is for. For everything FLAC vs MP3, the browser tool has you covered.