BPM Finder

How to use the BPM key finder

1. Drop a song into the box above or tap Choose audio file.
2. Wait a few seconds while your browser works out the tempo and key. Longer songs take longer.
3. If the tempo feels twice too fast or too slow, pick the other reading.
4. Press Play with clicks and listen. If the clicks sit on the beat, the reading fits.
5. No file? Use Tap tempo and tap along while the song plays.

When the result can be wrong

Both numbers are estimates worked out from the sound. These are the cases we saw go wrong or become unclear while testing:

Half time and double time

A beat at 70 BPM with busy hi-hats can also be counted as 140 BPM, and a 174 BPM drum and bass loop can read as 87. The finder can't know how you count, so it always shows both readings and lets you choose.

Songs that speed up or slow down

One number can't describe a song whose tempo changes. For files of 40 seconds or longer, the finder also checks 20-second sections, and if they disagree by more than 4% it shows the range it found.

Music without a steady beat

Sustained pads with no drums gave a weak tempo reading. When the confidence says Weak, don't rely on the number.

Tracks with few pitched notes

Drum-only tracks and noise don't have a key, so the finder says so instead of guessing.

Major or its relative minor

C major and A minor use the same notes, so they are easy to mix up. The next closest keys are listed under the result. The finder gives one key for the whole file, even if the song changes key.

BPM and key finder FAQ

Is my song uploaded?

No. Your browser decodes and analyzes the file on your device. The only files your browser downloads are this page and its two scripts, both from this site.

Can I use it as a song key finder only?

Yes. Every file gets a key reading next to the tempo, as a major or minor key, for example A minor or F♯ major.

What does the confidence line mean?

For tempo, it describes how much the best tempo stands out from other tempos in the same file. For key, it describes how well the notes match the key and how far ahead it is of the next closest key. It is not a chance of being right.

How was it tested?

With test tracks we made at known tempos and keys: a click track, drum loops, a tempo change, chord progressions, sustained pads and noise. It has not been checked against a large collection of real recordings, so use Play with clicks to check the result by ear.

How does tap tempo work?

It divides the time from your first tap to your last by the number of beats in between. Tap for longer to even out small timing errors. A pause of more than 2.5 seconds starts a new count.

Is there a file size or length limit?

This page sets none. The decoded song is kept in memory while you listen, so very long files need more memory and the practical limit depends on your device.