BPM and key finder
Get the tempo, key and Camelot code of a track in seconds. No upload and no daily limit: the analysis runs in your browser, so the file stays on your device.
Your file never leaves your device. Everything is measured in this browser tab.
How to use it
- Choose a song file or drop it on the panel: WAV, AIFF, FLAC, MP3, M4A or OGG.
- Read the tempo. The big number is the BPM rounded to a whole beat; the line below gives one decimal and how clear the pulse was.
- Read the key and Camelot code. Use the code to pick tracks that mix well: the same number, one step either way, or the same number with the other letter.
How it works
Tempo. The track is folded to mono and reduced to about 11 kHz. A detector looks for the moments where energy rises in 24 frequency bands, which gives a pulse curve of the drums, plucks and chord changes. The curve is compared with itself at every delay from 55 to 215 BPM, beats that repeat over many bars are rewarded, and a fine search over up to 64 beats settles the tempo to a tenth of a BPM.
Key. The spectrum from C2 to C7 is folded into the 12 pitch classes for every 0.7 seconds of audio, then summed over the song. That profile is compared with the Krumhansl–Kessler profiles for all 24 major and minor keys; the closest match wins.
Both are read from the first 15 minutes of the file. Loudness is measured over the whole file.
Half time, double time
A song at 70 BPM and the same song counted at 140 BPM have the same pulse; which one is “right” depends on the genre and on whether you count the snare or the hi-hat. Hip-hop is usually counted slow, drum and bass fast (174, not 87). The finder prefers tempos near the middle of the usual range and always shows the half and double, so pick the one your DJ software or DAW expects.
Tempos that drift (live drummers without a click, rubato piano) have no single BPM. The finder reports the average and marks the result as less certain.
Camelot wheel
Each key has a number from 1 to 12 and a letter: B for major, A for minor. Neighbours on the wheel share most of their notes, so they mix smoothly.
| # | Major (B) | Minor (A) |
|---|---|---|
| 1 | 1B B major | 1A G♯ minor |
| 2 | 2B F♯ major | 2A E♭ minor |
| 3 | 3B D♭ major | 3A B♭ minor |
| 4 | 4B A♭ major | 4A F minor |
| 5 | 5B E♭ major | 5A C minor |
| 6 | 6B B♭ major | 6A G minor |
| 7 | 7B F major | 7A D minor |
| 8 | 8B C major | 8A A minor |
| 9 | 9B G major | 9A E minor |
| 10 | 10B D major | 10A B minor |
| 11 | 11B A major | 11A F♯ minor |
| 12 | 12B E major | 12A C♯ minor |
When the result can be wrong
- Songs that change key, or sit between a major key and its relative minor (C major and A minor share every note), can come out as the neighbour. The “Next closest key” line shows the runner-up.
- Tracks without a steady beat, very sparse arrangements, or files shorter than about 6 seconds may have no measurable tempo.
- Detuned recordings (for example tuned to A = 432 Hz) are read as the nearest key in standard tuning.
Questions
On music with a steady beat it lands within a fraction of a BPM. The common mistake is the octave: reporting 70 instead of 140, or 87 instead of 174. The half and double are always shown so you can pick the one that matches how the song is counted.
It measures how much energy each of the 12 pitch classes has over the song and compares that profile with the typical profile of every major and minor key. The best match is the key; the second best is shown too.
A DJ notation for keys: numbers 1 to 12 around a wheel, B for major and A for minor. Tracks with the same code, a code one step away, or the same number with the other letter usually mix without clashing.
No. Everything runs in your browser, so there is no account, no upload and no daily limit.
No. The file is opened and analysed on your device; nothing is sent to our servers.
WAV, AIFF, FLAC, MP3, M4A (AAC/ALAC) and OGG. WAV and AIFF up to 1.5 GB; compressed files up to 300 MB.
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