Bar

A Bar (or measure) is the unit scale of time in a piece of music.

The length of music can be expressed in bars but it doesn’t inherently hold any metric of time unless the BPM is mentioned.

$$\text{Length of Song}=\text{No. of Bars}\times \frac{\text{Time Signature}}{BPM}[\text{Minutes}]$$

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References

https://www.mightyexpert.com/what-is-a-bar-music/