Bars to seconds calculator

A bar lasts beats-per-bar divided by tempo, times sixty. At 120 BPM in 4/4 a bar is exactly two seconds, so eight bars is sixteen.

That 120 BPM coincidence — two seconds a bar, thirty bars a minute — is why so much dance music sits there or near it: the arithmetic is trivial and sections land on round numbers. It matters for anything timed against picture. A 30-second advert is exactly 15 bars at 120 in 4/4, and if your track is at 128 it is 16 bars with a second left over, which is the sort of thing that gets discovered late. Worth noting for video work that this assumes constant tempo; anything with a tempo map needs the sections added up separately.