Change the tempo of a song to the BPM you need - to match your running pace, beatmatch two tracks for a mix, slow a piece down to learn it or fit a dance routine - without the key moving. Drop a song in and the page estimates its BPM from the beats it hears; type the BPM you want and it works out the tempo (120 to 128 BPM is 106.7%) and plays the song at that speed straight away, in the same key. The tempo is changed by Signalsmith Stretch, a high-quality time-stretching library, so the result does not wobble or echo the way a cheap speed change does. It is free to use, with no account and no upload limit, and it runs entirely in your browser: nothing is uploaded, and while the page stays open, a feature you have already used keeps working offline.
- How accurate is the BPM it finds?
- It is an estimate, worked out from where the beats fall in the first minutes of the song. For music with a steady beat - pop, dance, rock, hip-hop - it is usually right to within a fraction of a BPM, but it can land on half or double the tempo people count, most often for fast drum and bass or a slow ballad; press ½ or ×2 then. A song whose tempo drifts, such as a live recording, gets an average, and speech or ambient music may get none. If you know the BPM, type it over the estimate.
- How do I work out the tempo for a new BPM?
- Divide the BPM you want by the song's BPM and multiply by 100: 120 BPM to 128 BPM is 106.7%, and 140 BPM to 70 BPM is 50%. Type both numbers here and the page does the sum and sets the tempo for you.
- Does changing the BPM change the key of the song?
- No. The tempo is changed by time-stretching, which leaves the pitch where it was, so a song taken from 100 to 120 BPM stays in its key. For the old-record effect, where both go up together, raise the pitch too: 120% goes with about +3.16 semitones.
- Can I match the BPM of two songs for a mix?
- Yes. Open the first song and note its BPM, then open the second and type the first one's BPM as its target, and save it. Both then play at the same tempo. Small changes of a few percent sound the most natural.
- What BPM suits running or walking?
- Many runners pick music close to their step rate: roughly 160-180 steps a minute when running, and 100-130 when walking briskly. Set the target to your step rate, or to half of it for a song that feels slower, and the page sets the tempo to match.