Varispeed calculator: BPM to pitch in semitones

A varispeed calculator converts a tempo change into a pitch change. On tape, vinyl or a sampler without time-stretch, speed and pitch move together, and the pitch shift in semitones is 12 × log2(new BPM ÷ original BPM). Slowing a track from 120 to 100 BPM drops it 3.16 semitones (316 cents); speeding a beat from 140 to 150 BPM raises it 1.19 semitones. Enter any two tempos above and the readout gives semitones, cents, percent and the speed ratio.

The same math runs in every direction: as a BPM to pitch calculator when you want to know how far a varispeed move will detune a song, as a pitch to tempo calculator when you have pitched a sample and need its new BPM, and as a percent to semitones table when a tape machine, turntable or speed slider only shows a percentage. The tables below cover all three so you can read the answer without typing.

Tape and vari-speed: change speed, change pitch

On tape, speed and pitch are the same control. Slow the machine down and the music drops in pitch and tempo at the same time; speed it up and both rise. A 15 ips tape played at 7.5 ips is exactly half speed and an octave down; a 33⅓ rpm record played at 45 rpm runs 35% fast and 5.20 semitones sharp. This calculator shows how far the pitch moves when you change the tempo, so you can recreate the classic vari-speed sound or match a sample to a new BPM.

The formula

The speed ratio is new BPM divided by original BPM. The pitch shift in semitones is twelve times the base-2 logarithm of that ratio, and cents are semitones times 100. Halving the tempo drops the pitch a full octave; doubling it raises an octave.

The shift is logarithmic, which is why percent and semitones never line up neatly: +10% is +1.65 semitones but −10% is −1.82 semitones, because 1.10 and 0.90 are not reciprocals. One semitone up is +5.95% speed; one semitone down is −5.61%. The pitch and semitone calculator works from the semitone side if you already know the interval you want.

Tempo change in percent to semitones and cents

For tape machines, turntables and DJ pitch faders that read in percent. Faster and slower are listed separately because the slower side always moves slightly further.

A DJ pitch fader at +6% is one semitone up almost exactly (+1.01), and −6% is −1.07 semitones, so at ±6% a record is already a full semitone away from its original key.

BPM to pitch: common tempo pairs

Each row is what happens to the key of a sample or a song when you play it at the new tempo without time-stretching. Positive is sharp, negative is flat.

The last row is the half-time trick: 140 and 70 BPM are the same groove counted differently, so a 140 BPM trap loop slowed to 70 on tape is a full octave down, while simply re-counting it at 70 changes nothing. The hip hop key and tempo guide covers why those two numbers describe one beat. To find the starting BPM of a sample you did not make, run it through the BPM detector first.

Pitch to tempo: semitones to BPM

Pitched a sample by ear and need the new tempo for the project? Multiply the original BPM by 2 to the power of semitones ÷ 12. Three common starting tempos are worked out here; the speed column applies to any BPM.

Rule of thumb for keeping a sample in tune: stay within one semitone, which means a tempo window of −5.61% to +5.95%. A 120 BPM loop fits projects from 113.3 to 127.1 BPM before the key moves a full step; a 140 BPM loop covers 132.1 to 148.3. Beyond that, either time-stretch or accept the new key and check it with the song key finder.

Slowed + reverb and nightcore numbers

Both edits are plain varispeed. Most slowed + reverb versions run at 0.8× to 0.9× speed, which is −1.82 to −3.86 semitones, and nightcore edits usually run 1.2× to 1.3×, which is +3.16 to +4.54 semitones. The table shows what each common multiplier does to pitch, to a 120 BPM song and to a 3:30 running time.

Worked example: a song in A minor at 120 BPM slowed to 0.85× lands at 102 BPM and 2.81 semitones down, which is 19 cents sharp of F♯ minor. The reverb is added after the slowdown, and because the tempo changed, a quarter-note delay that was 500 ms at 120 BPM is 588 ms at 102 BPM; the delay and reverb time calculator gives the new values for any note length. The audio speed changer applies the speed change to a file in your browser, and the song length calculator shows the new running time from bars and the new BPM.

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