Convert AAC audio to an MP3 that plays on any device or player, right in your browser. Choose the bitrate and download — nothing is uploaded.
AAC is the codec inside M4A files and most streamed and purchased audio — technically a bit more efficient than MP3 at the same bitrate. A raw .aac (ADTS) file is that same codec without the MP4 wrapper, and it's exactly what some devices and editors won't touch. Converting AAC to MP3 swaps a marginally-better-but-fussier format for the one with the widest support of any audio format there is.
Both are lossy, so this is a transcode: pick 320 kbps so the extra encoding pass doesn't audibly soften the result, and always convert from the best AAC source you have rather than a chain of re-compressions. Everything runs in your browser with no upload. If your file is actually an .m4a, the dedicated M4A to MP3 page frames it that way; for other targets there's the full audio converter.
AAC is a newer codec that's slightly more efficient than MP3 — a bit more quality at the same bitrate — and it's what most streamed and purchased audio uses, usually inside an M4A container. A raw .aac (ADTS) file is that same codec without the wrapper. MP3 is older and marginally less efficient, but it has the widest device and software support of any audio format, which is exactly why you'd convert to it.
It's a lossy-to-lossy transcode, so there's some loss, but it's minor if you keep the MP3 bitrate high — 320 kbps. The bigger risk is compounding: converting an already low-bitrate AAC to a low-bitrate MP3 stacks two rounds of compression audibly. Convert from the best AAC source you have, at a high MP3 bitrate, and the result holds up well.
Almost — an .m4a file is AAC audio inside an MP4 container, while a .aac file is the raw AAC stream. Both convert to MP3 the same way here. If your file is specifically an .m4a, the dedicated M4A to MP3 page frames it that way, but this page will convert it too. Either way it's decoded and re-encoded entirely in your browser, with nothing uploaded.
An MP3's size is set by the bitrate you pick multiplied by the length, not by the source file. If your AAC is 128 kbps, the default 192 kbps MP3 comes out about 50% larger, and 320 kbps makes it two and a half times the size. The extra bitrate can't add detail; it just keeps the second encode from losing as much. The estimated size shows before you convert, and 128 kbps would keep it about the same size, at some cost in quality.
Use the video to audio tool for that. Most MP4 and MOV videos store their sound as AAC, and that tool pulls the soundtrack out of MP4, MOV, MKV, WebM, and other video files and saves it as MP3 or WAV in one step. It uses Vocal Cut's audio engine, a one-time download of about 20 MB to your browser that is cached afterward, and the video never leaves your device. This page is for audio-only .aac and .m4a files.