Loop Tempo Calculator
Turn a trimmed loop length into BPM, then calculate the duration and playback ratio needed for a new tempo. Choose the beat unit explicitly, including dotted quarters in 6/8.
Measure from a downbeat to the downbeat after the last complete bar. Exclude count-ins, leading silence and reverb tails. A pickup or changing tempo needs separate handling. This tool calculates settings; it does not edit audio.
Count the loop before calculating
A clean loop needs two known boundaries: the start of its first full bar and the start of the next bar after its last full bar. Enter the time between those points. Counting a four-bar phrase as two bars halves the answer; including a reverb tail makes the answer too slow. Use Tap Tempo as an independent listening check, then read the loop BPM guide.
The numerator is the top number of the time signature and the denominator names the written note value. This is separate from the BPM beat unit. In 6/8, six eighth notes occupy a bar, often felt as two dotted-quarter beats. Most DAW tempo fields count quarter notes. The result shows both interpretations explicitly. The 6/8 and 3/4 guide explains the accent pattern.
From seconds to tempo
Quarter notes in the loop = bars × numerator × 4 / denominator. Counted beats = quarter notes / beat-unit length, measured in quarters. BPM = 60 × counted beats / seconds.
Four bars of 4/4 lasting eight seconds contain sixteen quarter-note beats, giving 120 BPM. Four bars of 6/8 lasting eight seconds contain eight dotted quarters, giving 60 dotted-quarter BPM, or 90 quarter-note BPM. These are timing calculations, not a claim that the music has one uniquely correct metrical interpretation.
Match a new tempo without reversing the ratio
Playback speed = target BPM / original BPM. Target duration = original duration / playback speed. New duration as a percentage of the original is 100 / playback speed. Moving from 120 to 100 BPM gives 83.333% speed and 120% duration. A software control called “stretch” may mean either quantity; read its definition before entering a percentage.
Varispeed changes pitch with playback speed. Its shift in semitones is 12 × log₂(speed ratio). Pitch-preserving time stretch aims to hold pitch steady instead. The Ableton warping manual distinguishes Re-Pitch from its other algorithms. The calculator reports the varispeed shift for comparison; it does not promise artifact-free processing.
Check the grid after editing
Use the exported settings in your audio editor, audition several repetitions and compare the last downbeat with the grid. A correct average duration does not remove drift within a live performance. Trim errors and variable tempo can need local markers rather than one global ratio. Use the metronome for a pulse reference and the note-values guide when the counted unit is uncertain.
Questions
Does this detect the tempo of an audio file?
No. You supply the number of complete bars, meter and duration. The result is an average tempo under those assumptions. No file is loaded or analysed.
Why do I get 90 and 135 BPM for the same 6/8 loop?
Ninety dotted-quarter beats per minute equals 135 quarter-note beats per minute. A 6/8 bar contains two dotted quarters or three quarters. The elapsed time is identical; the beat unit differs.
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