BPM finder for audio files
Drop in an MP3, M4A or WAV – a few seconds later you see the tempo in beats per minute. Honestly, with a ± range, because not all music has one clear tempo.
How it is calculated
DJs, dancers, musicians practising or runners matching music to their stride all want to know a track’s tempo. This tool estimates beats per minute (BPM) straight from the file – locally, without the music leaving your device.
How it works
- Drop in or choose an audio file. Analysis starts automatically.
- The tempo is shown at the top, with the uncertainty (±) and how reliable the estimate is below.
- If a second tempo is shown, it is often half or double – tap along briefly to decide.
How it is calculated
The file is resampled to 11,025 Hz mono. A short-time spectrum yields an “onset curve” that rises at every attack. Its autocorrelation shows at which interval attacks repeat. As in D. P. W. Ellis (2007), it is weighted with a window around 120 BPM, because people tend to perceive tempi in that region; this also gives the second, alternative tempo. The result is refined over multiples of the beat period. The uncertainty comes from comparing 20-second sections of the track.
Honest limits
Music without a clear beat – free-tempo classical, ambient, speech – gives an uncertain result or none. Half and double tempo often cannot be told apart by calculation. At most the first 6 minutes are analysed. We deliberately do not show a musical key, because we cannot determine it reliably enough.
Privacy
The file is processed only in your browser and is not uploaded.
Frequently asked questions
How do I find the BPM of a song?
Choose the file here – the tempo is calculated automatically and shown with its uncertainty. Free and nothing is uploaded.
Why does the tool sometimes show a second tempo?
Because half and double tempo can fit equally well, for example 70 and 140 BPM. Which one is meant depends on how you feel the basic beat.
How accurate is the BPM detection?
In our tests with steady beat patterns the error was below 1 BPM. For real music, the ± range and the confidence level show how certain each result is.
Does it detect the key as well?
No. Key detection would not be reliable enough, so we leave it out.
Sources and legal basis
- D. P. W. Ellis: Beat Tracking by Dynamic Programming. Journal of New Music Research 36(1), 2007, S. 51–60 (Onset-Stärke, Tempo-Schätzung, Abschnitt 3)
- MDN – BaseAudioContext.decodeAudioData()
- MDN – OfflineAudioContext (Web Audio API)
As of:
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