How this calculator works
A bar has a fixed number of beats, and the tempo fixes how long each beat lasts. In 4/4 the bar holds four quarter-note beats, so at 120 BPM each beat is half a second and each bar is two seconds. Thirty-two bars therefore last 64 seconds. In 6/8 the bar holds six eighth notes, which is three quarter-note beats, so a bar at 120 BPM lasts 1.5 seconds. Tempo is usually given for the beat the time signature names, which is why the same BPM gives different bar lengths in different signatures.
Formula
quarter-note beats per bar = numerator x 4 / denominator. quarter note (s) = 60 / BPM. bar length = beats per bar x quarter note. duration = number of bars x bar length. bars = duration / bar length.
Worked example
A 32-bar song in 4/4 at 120 BPM: each bar is 4 x 0.5 = 2 seconds, so the song lasts 64 seconds, just over a minute. The same 32 bars at 90 BPM last 32 x 4 x (60/90) = 85.33 seconds. A 10-bar phrase in 3/4 at 90 BPM lasts 10 x 3 x 0.667 = 20 seconds.
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Frequently asked questions
Does a tempo marking always match the denominator?
Usually the tempo is written for the beat that the time signature counts, which is the denominator, except in compound time such as 6/8 where the felt beat is a dotted quarter even though the written unit is an eighth. This page measures the written unit, which matches how most notation software and tempo maps work.
Why is the real track shorter or longer?
A recording may add a count-in, ritardando, fermatas or an extra bar at the end. Tempo may also change during the piece. The calculation assumes a constant tempo and exactly the stated number of bars, so treat it as the musical running time rather than the file length.
How do I convert this to a click track length?
The duration is the time from the first beat to the end of the last bar, so it is also the length of a click track with no count-in. Add one extra bar for a count-in and any silence you want at the start or end.
Can I use this for a set list?
Yes. Add the durations of the songs and compare with the slot. Remember that live tempos drift and that applause and talk time are not counted here, so leave a margin for a concert set.