Music Duration Calculator (song length from bars, time signature and BPM)

Understanding the music duration calculator — concept and principle

This calculator works out how long a piece of music lasts from the number of bars, the beats per bar, the tempo in BPM and the number of times it is played. Composers, arrangers, band leaders and video editors use it to fit music to a time slot or to plan a set list.

Beats into seconds: with the default inputs the result is 2 min 8 s (= 128 seconds).

How it is calculated

One beat lasts 60 ÷ BPM seconds.
Total beats = bars × beats per bar × times played.
Duration (s) = total beats × 60 ÷ BPM, shown as h:mm:ss.
Length of one bar = beats per bar × 60 ÷ BPM; one beat in ms = 60,000 ÷ BPM.
Bars per minute = BPM ÷ beats per bar.

The principle

A metronome mark says how many beats fit into a minute, so each beat has a fixed length. Counting the beats in the piece and multiplying by that length gives the duration. The key is to count the same beat the tempo refers to. In 6/8 marked at a dotted-quarter pulse there are two beats per bar, not six. Repeats multiply the whole count. Real performances add fermatas, ritardandos and tempo changes, which this simple model does not include.

Worked example

Default inputs: 64 bars, 4 beats per bar, 120 BPM, played once.

One beat = 60 ÷ 120 = 0.5 s = 500 ms.
Total beats = 64 × 4 × 1 = 256.
Duration = 256 × 0.5 = 128 s = 0:02:08.
One bar = 4 × 0.5 = 2 s; bars per minute = 120 ÷ 4 = 30.

How to read the result

Use the duration to check whether a piece fits a slot, such as a 2-minute film scene or a 3-minute radio edit. To lengthen or shorten it, change the tempo slightly or add or cut bars: at this tempo every 4-bar phrase is 8 seconds. Live performances often run a little longer than the arithmetic because of breaths and endings.

Common mistakes

Counting eighth notes in 6/8 when the tempo is given per dotted quarter.
Forgetting repeats and da capo sections.
Using a tempo that changes partway through as if it were constant.
Including pickup bars as full bars.

Keep in mind: The result is the mathematical length at a steady tempo. Expressive timing and tempo changes make real performances differ.

Frequently asked questions

How long are 64 bars at 120 BPM in 4/4?

256 beats at 0.5 s each, which is 2 minutes 8 seconds.

How long is one beat at 90 BPM?

60 ÷ 90 = 0.667 seconds.

How do I count beats in 6/8?

Use the beat the tempo marking refers to; at a dotted-quarter tempo that is 2 per bar.

Sources: Definition of the metronome mark: one beat = 60 ÷ BPM seconds (e.g. Grove Music Online, "Metronome")

Checked 9 Nov 2026. Definition of the metronome mark (beats per minute): one beat = 60 ÷ BPM seconds — standard value; 1 min = 60 s.

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