Bitrate
Size follows the bitrate
A 4-minute song is about 9.6 MB at 320 kbps, 3.8 MB at 128 kbps and 1.9 MB at 64 kbps. The length stays the same; each second just takes fewer bits.
MP3 Compressor
Make MP3 files smaller online, free. Lower the bitrate for podcasts, voice notes and music. No sign-up.
- Free to use
- No file stored beyond 1 hour
- Encrypted over TLS 1.2/1.3
- No watermarks
Drag and drop your files here or click to upload.
Maximum file size is 1GB
Like RunConvert? Set us as a preferred source on Google.
Add to Preferred SourcesHow to compress an MP3
Three steps, in your browser. Nothing to install.
- 01
Add your MP3s
Drop up to 20 MP3 files, or paste a link.
- 02
Pick a bitrate
Every file starts on Balanced (96 kbps). Open a file's settings to make it smaller or keep more quality, for one file or all of them.
- 03
Compress and download
Each file stays an MP3, so it plays everywhere it did before.
Which bitrate should I pick?
Pick by what's in the file: speech needs far less than music. A file already at or below the bitrate you pick won't get smaller.
- Smallest file (64 kbps)Speech, lectures and voice notes. Music sounds noticeably thinner.Voice notes
- Balanced (96 kbps)DefaultPodcasts and audiobooks sound clear at about a third of a 320 kbps file.Podcasts
- Best quality (128 kbps)Music that still sounds good on headphones and in the car.Music
How the MP3 gets smaller
An MP3's size depends almost only on its bitrate and its length. Lowering the bitrate is the whole trick.
Content
Speech needs less than music
Voices sit in a narrow range of frequencies, so podcasts and lectures stay clear at 64 to 96 kbps. Music keeps its detail better at 128 kbps.
- Format
- MP3
- Bitrates
- 64, 96 or 128 kbps
- Files
- Up to 20 files, 1 GB each
- Output
- MP3
Starting from WAV, M4A or a video?
Convert straight to a small MP3 instead:
More free audio tools
Frequently asked questions
Common questions about compressing MP3 files with RunConvert.
Yes, free and without a watermark or sign-up.
Yes, a little: MP3 is lossy. 128 kbps is fine for most listening, 96 kbps for speech and podcasts, and 64 kbps for voice recordings.
It was already at or below the bitrate you chose. Pick a lower setting. The download page shows the change for each file.
Up to 20 files at a time, up to 1 GB each.
They are encrypted in transit, used only for your compression, and deleted automatically after a few hours.
Ready to compress your MP3?
Free, no sign-up, no watermark.