BPM Key Finder

How to find the BPM and key of a song

1. Open the song. Press Choose audio, or drop a file on the box. Video files work too: the tool uses their sound.
2. Read the result. The tempo appears in beats per minute (BPM), with one decimal, and the key as a name such as A minor, with its Camelot code.
3. Pick half-time or double-time if needed. Tempo detection can land on half or double the speed you count. The three buttons switch between them.
4. Check it by ear. Press Play with Click on each beat ticked. If the clicks stay on the beat all the way through, the tempo is right.

How it works

• Tempo. The tool looks for moments where the sound suddenly gets louder in some frequencies (drum hits, notes starting), about 86 times a second. It then measures how strongly that pattern repeats at every tempo from 40 to 240 BPM. A mild preference for tempos near 120 BPM settles ties between half and double speed; librosa’s tempo estimator uses the same kind of preference. The winning tempo is then fine-tuned across up to 64 beats, which is why it can show a decimal.
• Key. The tool adds up how much of each of the 12 notes (C, C♯, D … B) the song contains, after correcting for songs that aren’t tuned to A = 440 Hz. It then compares that profile with the Krumhansl–Kessler key profiles, which come from listening experiments on how well each note fits a key, and picks the closest of the 24 major and minor keys.
• Tempo by section. For songs longer than 30 seconds, the tempo is measured again in 20-second sections, so you can see whether it stays steady.

Sources (read 27 Oct 2026): the key profile values as listed in Robert Hart’s key-finding article, which cites Carol Krumhansl’s Cognitive Foundations of Musical Pitch; the librosa tempo documentation for the 120 BPM prior; the Camelot wheel page from Mixed In Key for the Camelot codes.

How accurate is it?

We tested the same analysis code on audio with a known tempo and key, made for the test. That proves it works on clean material; real songs are harder, and we haven’t measured it on a library of commercial tracks.

The key is labelled an estimate for a reason. Songs that change key, use modes, or sit between a major key and its relative minor (C major and A minor share the same notes) are often called differently by different tools, and by musicians too. The two next-closest keys are shown so you can compare.

Half-time, double-time and the Camelot code

A drum and bass track at 174 BPM can feel like 87 BPM, and a slow ballad at 70 BPM can be counted at 140. Both are correct ways to count the same music, so the tool shows the half and double next to the main result. DJ software usually expects the faster count for dance music. The Camelot code (for example 8A for A minor and 8B for C major) is the key notation DJs use for harmonic mixing: keys with the same number, or a number one apart, usually mix well.

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