BPM & Key Finder
Find the tempo and key of any song in seconds. Drop an MP3, WAV or M4A — it's analysed in your browser and never uploaded.
How it works
Your file is decoded by your browser's Web Audio engine, mixed down to mono and resampled to 22 kHz. For tracks longer than two minutes, we analyse the middle 120 seconds, which skips intros and outros that often have no beat.
For tempo, we compute an onset-strength envelope: the spectral flux of short overlapping frames, which spikes on every kick, snare and transient. Autocorrelating that envelope reveals how often the pattern repeats, and we score every tempo from 60 to 200 BPM in 0.1 BPM steps, with a mild preference for the 85–175 BPM range most music lives in.
For key, we pick out the spectral peaks of each frame and fold their harmonics back onto the note that produced them, so a note's overtones aren't mistaken for other notes. The resulting 12-note profile is compared with the 24 major and minor key profiles.
Confidence comes from the analysis itself: how far the winning tempo stands above the others, and the margin between the best and second-best key. Everything runs in a background worker, so the page stays responsive.
What is the Camelot wheel?
| # | Minor (A) | Major (B) |
|---|---|---|
| 1 | 1A · Ab minor | 1B · B major |
| 2 | 2A · Eb minor | 2B · F# major |
| 3 | 3A · Bb minor | 3B · Db major |
| 4 | 4A · F minor | 4B · Ab major |
| 5 | 5A · C minor | 5B · Eb major |
| 6 | 6A · G minor | 6B · Bb major |
| 7 | 7A · D minor | 7B · F major |
| 8 | 8A · A minor | 8B · C major |
| 9 | 9A · E minor | 9B · G major |
| 10 | 10A · B minor | 10B · D major |
| 11 | 11A · F# minor | 11B · A major |
| 12 | 12A · C# minor | 12B · E major |
Frequently asked questions
Is it free?
Yes. The BPM and key finder is free, with no sign-up and no limit on how many tracks you analyse.
Are my files uploaded?
No. Your track is decoded and analysed inside your browser with the Web Audio API. The file never leaves your device.
How accurate is it?
On music with a steady beat and a clear tonal centre, tempo is usually within 1 BPM and the key matches what DJ software reports. Ambient tracks, live recordings with tempo drift and songs that change key are harder; each result shows a confidence label so you know when to double-check by ear.
Why does it show half or double my BPM?
Tempo is ambiguous: a trap beat at 140 BPM feels like 70, and drum & bass at 174 can read as 87. Use the ½× and 2× buttons to switch to the tempo you count along to.
What is a Camelot key?
The Camelot wheel numbers the 24 keys from 1 to 12 with A for minor and B for major. Keys next to each other on the wheel (same number, or ±1 with the same letter) mix together harmonically.