About the Tempo Change Calculator
This tempo change calculator answers the questions that come up whenever a song has to move from one BPM to another: how big is the change in percent, what time-stretch ratio should go into the DAW or DJ software, how long will the track run afterwards, and how far would the pitch move if you simply sped the audio up instead of stretching it.
It is built for DJs beat-matching two records, producers fitting a sample or an acapella to a project tempo, editors cutting music to a fixed duration, and musicians practising a piece slower than performance tempo. Enter the original BPM and either a target BPM or a target length, and the tool works out the rest.
With key lock or time-stretching on, only the tempo and length change. Without it (varispeed, turntable or tape), pitch changes by the semitone figure shown, because every frequency is scaled by the same ratio as the tempo.
With the default inputs, the tempo change is 6.667%. Change any value above to recalculate instantly.
How to use the tempo change calculator
- 1Enter the original tempo of the song in BPM.
- 2Choose whether you are aiming for a new BPM or a new running time.
- 3Enter the target BPM, or the original and target lengths as m:ss.
- 4Read the percent change and time-stretch ratio to dial into your software.
- 5Check the semitone shift if you cannot use key lock.
Formula and method
Tempo and running time are inversely proportional: playing a song r times faster multiplies its BPM by r and divides its length by r. When you set a target length instead of a target BPM, the ratio is simply old length ÷ new length. A beat lasts 60,000 ÷ BPM milliseconds.
If the change is done by resampling (varispeed, turntable, tape), every frequency is also multiplied by r, which equals a pitch change of 12 × log₂(r) equal-tempered semitones. Time-stretching algorithms avoid that pitch change, but large stretches (beyond roughly ±10–15%) can add audible artefacts.
- r
- Tempo ratio (new tempo ÷ original tempo)
- BPM
- Beats per minute
- semitones
- Pitch shift if tempo is changed without key lock
Worked examples
Mix a 120 BPM track into a 128 BPM set
128 ÷ 120 = 1.0667, a 6.67% speed-up. The 225-second song shrinks to 225 ÷ 1.0667 ≈ 210.9 s (about 3:31), and without key lock it would rise 12 × log₂(1.0667) ≈ 1.12 semitones.
Slow a solo down for practice
126 ÷ 168 = 0.75, a 25% slowdown. A one-minute passage takes 60 ÷ 0.75 = 80 seconds. Slowing it on a tape machine would drop it almost 5 semitones, so practice apps time-stretch instead.
Fit a 3:45 song into 3:30
To fit 225 seconds into 210, the tempo ratio is 225 ÷ 210 = 1.0714, a 7.14% speed-up. The 96 BPM song ends up at about 102.86 BPM.
Frequently asked questions
How do I calculate BPM percent change?+
Divide the new BPM by the old BPM, subtract 1 and multiply by 100. Going from 120 to 126 BPM is 126 ÷ 120 = 1.05, a 5% increase.
Does changing tempo change pitch?+
Only when the audio is resampled, as on a turntable or with varispeed. Time-stretching with key lock changes tempo and length while keeping the original key.
How much can I time-stretch before it sounds bad?+
Modern algorithms usually stay clean within about ±10%, and vocals and solo instruments reveal artefacts sooner than drums. Results depend heavily on the material and algorithm.
What is the difference between tempo ratio and length ratio?+
They are reciprocals. A 5% faster tempo (ratio 1.05) gives a length ratio of 1 ÷ 1.05 = 95.238%. Some DAWs ask for one, some for the other.
How many BPM is one semitone?+
It depends on the starting tempo: a semitone is a 5.946% change, so at 120 BPM it is about 7.1 BPM, and at 90 BPM about 5.4 BPM.