Relationship between bpm, time and bars (or measures)
There are many automatic calculators online that can do these convergence, but it is good to know the formula, nevertheless.
Seconds = ((Bars x beats per bar) ÷ BPM) x 60)
you can flip things when you need to find one or the other parameter.
Let’s say, you have to write a blues progression for a TV advt. and required to be exactly 45 seconds long.
The standard blues progression is 12 bars (or measures) and the time signature (that is beats per bar) is 4.
So we have all the variables to calculate my BPM for this track. Using the formula above.
BPM= ((12 bars x 4 beats per bar)÷ 45s ) x 60 = 64 bpm So if I want to play it twice within the 45s, then either do the calculation again with 24 instead of 12 bars, or simply multiply the bpm by 2 = 128bpm