Free BPM & Key Finder

Worked example

Press "Try a sample". The tool builds a short loop at exactly 120 BPM in A minor, loads it and starts analysing at once, so there is no "Analyze track" button to press. The "Tempo (BPM)" and "Key" boxes fill in, and you can check them against that known answer. For A minor the Key box adds "Camelot: 8A", and "Compatible keys for harmonic mixing" lists "8B · C major", "7A · D minor" and "9A · E minor". Below the readout sits "Tap tempo", which also works with no file. Tap it every half second: after the second tap it reads "Tap tempo · 120 BPM", because 60 divided by 0.5 is 120. Wait more than 2 seconds and the count starts again.

Which settings to use, and the limits

• Give it a file, or skip the file and tap. The drop zone takes one audio or video file, and analysis starts as soon as it lands. For a video, the page decodes its sound track. The whole file is decoded in memory, so a file is refused above a device limit: about 2 GB on a normal computer, 1 GB on one reporting 4 GB of memory or less, and 400 MB on a phone or tablet. If you only want the tempo of music playing somewhere else, the "Tap tempo" button on the first screen needs no file.
• Fix half-time and double-time with the two small buttons. Tempo is always folded into the range 60 to 180 BPM, so a track at 200 BPM can only appear as 100. The "×½" and "×2" buttons (named "Show half-time tempo" and "Show double-time tempo" for screen readers) show half or double the result, rounded to 0.1, and pressing the same button again returns to the original. The page says "Sounds off? Half/double-time errors are common." Tap tempo uses the same 60 to 180 range.
• Read the key together with its trust label. Beside "Confidence" you see a percentage and a pill. The percentage is how well the best key profile fits, scaled to 0 to 100. The pill is the better guide, because it compares the winner with the runner-up: a gap of 0.12 or more is "Strong match", 0.05 up to 0.12 is "Likely", and anything smaller is "Ambiguous". Unless the match is strong, a line such as "Close second: A minor" names the other candidate. A major key and its relative minor often score almost the same, so check both by ear.
• Use the Camelot code for harmonic mixing. The code is a number from 1 to 12 plus A for minor or B for major, so A minor is 8A and C major is 8B. "Compatible keys for harmonic mixing" lists three neighbours: the same number with the other letter (the relative key), one step down the wheel and one step up, and the wheel wraps from 12 to 1. For 8A that gives 8B · C major, 7A · D minor and 9A · E minor. Keys are written with sharps (C#, D#, F#, G#, A#), not flats.
• Know what gets analysed. Tempo comes from loudness peaks (onsets) found along the first channel of the track; the spacing of the steady ones is averaged. The key comes from up to 12 short windows spread over the middle 80 percent of the file, each about 0.74 seconds at 44.1 kHz, skipping near-silent ones. A clip shorter than one window is read once. The page warns that BPM and key are automatic estimates, especially for music with tempo changes or ambiguous tonality, so verify before relying on them.
• Tap along when the analysis misses. The "Tap tempo" button is on the first screen and again below every result. Tap in time with the beat; from the second tap it shows the BPM, as in "Tap tempo · 120 BPM". It uses the last 8 taps, and a pause of more than 2 seconds starts a fresh count, so you can stop and restart without reloading the page. Tapping does not change the file analysis above it.

Common problems and how to fix them

It says "Could not analyze this audio file. It may be an unsupported or corrupted format."

The tool decodes the file with the browser's built-in audio decoder, and any failure while decoding or analysing ends in this one message: a format the browser cannot decode, a damaged file, or possibly a file too large for the device's memory. Try the same track as an MP3 or WAV, for example by converting it with the Audio Converter, or analyse a shorter clip. After the message an "Analyze track" button appears so you can try again.

It says "This file is 620 MB, which is over the ~400 MB this device can analyze in the browser. Try a smaller file or a shorter clip."

The file size is compared with the device limit as soon as you add the file: about 2 GB on a normal computer, 1 GB on a computer reporting 4 GB of memory or less, and 400 MB on a phone or tablet. The limit is on file size, not on length. Cut the track down first, or use a compressed copy such as an MP3, which is much smaller than a WAV of the same music.

The "Tempo (BPM)" box shows "—" and the "×½" and "×2" buttons are missing.

The tempo finder needs at least two beat-like onsets to measure a spacing. A drone, a soft pad, speech or a very gentle intro can have none, and then the result is 0, which the page shows as a dash. The key is still shown. Try a clip with a clearer pulse, or tap the tempo yourself with "Tap tempo".

The tempo is twice or half what you expect.

The tempo is folded into 60 to 180 BPM, and the beat detector can lock onto half or double the pulse you count. Press "×2" or "×½" to see the other value; the page says "Sounds off? Half/double-time errors are common." A track at 200 BPM can only appear as 100, and "×2" shows 200. Pressing the same button again goes back to the original reading.

The key pill says "Ambiguous" and a line says "Close second: A minor".

The best and second-best key profiles scored within 0.05 of each other. This often happens when a major key and its relative minor use the same notes. Listen to where the phrases come to rest, or play the track against a keyboard. "Likely" means the gap is between 0.05 and 0.12; "Strong match" means 0.12 or more, and then no runner-up line is shown.

How it compares

This tool gives one tempo and one key for the whole file, estimated on your device. It does not draw a beat grid, follow tempo changes, split a track into sections or write the BPM and key into the file's tags. A DJ program or music editor with a beat grid lets you check and correct a result against the waveform; here your checks are the "×½" and "×2" buttons, the key trust label and "Tap tempo". Tempo is limited to 60 to 180 BPM. The key is matched against major and minor profiles only, using the first channel, so modal or modulating music can be misjudged. The page says your audio is analysed in your browser and nothing is uploaded.