What's the BPM
of this song?

It detects the note onsets in the first 30 seconds of your recording, then measures which beat grid they fit best — testing every tempo from 30 to 300 BPM and preferring the one where the most musical weight lands on the beat.

Because a song at 90 BPM genuinely correlates almost as well at 180 — autocorrelation can't always tell the pulse from its double. The estimator checks the musical relatives of its answer explicitly, but when you're in doubt, try half and double and see which your foot agrees with.

It measures the average tempo of what it hears, so a song that breathes — live drums, rubato piano, a ritardando — gets a single representative number marked as a rough estimate. That's honest: there is no one BPM to report.

It analyses the first 30 seconds of music, after any leading silence — long enough for a steady tempo to show itself. If a song changes tempo mid-way, the answer reflects how it opens.

Free, and nothing is kept because nothing is sent — the audio is decoded and analysed entirely in your browser, on your device. Close the tab and it's gone.