What Is A Bar In Music? (Explained Simply)

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  • What are bar lines, and how many bars belong?
  • How did composers save time when writing music?
  • We go deep into these common questions.

Talking about music can be really confusing. We’ve all been there at one time or another: at a rehearsal with your band or listening back to something a producer friend shared with you, at some point you have to refer to a specific point in the music.

Music doesn’t have locations, though; it is ephemeral, and when it’s not happening, it only exists in your imagination. So when a bandmate or an engineer says, “go back to bar 63” or “the second bar of the chorus” what are they talking about? Where does this bar exist? Have no fear: In this article, we will answer the question “what is a bar in music?” by addressing the music theory behind the use of the bar line in music so that you’ll never again get lost in these conversations.

We will go into depth to answer the following questions:  

  • What does the time signature have to do with a bar?
  • How do you know when a bar ends and another begins?
  • How many bars are in different parts of a song?

Time Signature

The time signature is the element of basic music theory that tells you how time is organized in a piece of music. In written music (the sort of music that can be written out as sheet music on the staff) the time signature goes at the very top left-hand corner of the staff and is expressed as two numbers. The top number is the number of beats in a single bar or measure, and the bottom number refers to the type of note duration that gets the beat.

Common time, or 4:4, is referred to as common because it is the most prevalent in Western art music. Most pop music and electronic music styles are in 4:4, but if you dive into metal, especially more technical metal genres, you will find plenty of exceptions to this generalization. The top 4 in common time refers to the four beats in a single bar, and the bottom 4 indicates that the beat is a quarter note. Thus, in 4:4 time there are 4 quarter-note beats in a single bar. In 4:1, on the other hand, there are four whole-note beats in a single bar.  

There are a lot of different time signatures out there besides common time. If you can take a look at the sheet music, there is no mystery: just look at the upper left-hand corner. If the time signature changes in the piece, it will be indicated after two bar lines on the staff. It is a little trickier to determine the time signature if you are just listening to the music without a visual, but you can typically figure out what you are listening to by listening for the pattern of strong beats and weak beats.

A measure will typically start with a strong beat and be followed by a pattern of weaker beats. As I write this, I am listening to Neurodelirium by Kaleikr, which features some very prominent 7:4 passages. You can tell you are listening to 7:4 music by the prominent downbeat on beat 1 of each 7-beat measure. Whether you prefer to count as 4 and then count out another 3 with a weaker downbeat or count the whole 7, the 7:4 feel is clear.

Bar Lines

Measures in written music occur between bar lines that separate each measure from the one that precedes it and the one that follows. These are like spaces between words, making it easier to keep track of where you are in a piece of music. Just as spaces did not always exist (just check out old Latin inscriptions), bar lines were not always written in music either, but both have certainly become indispensable conventions.  

As I mentioned earlier, the double bar line can be used to indicate a change in the time signature. It can also indicate the change in a key signature or just the end of a particular section of music.
Bar lines meant to indicate a repetition of one or more bars look like the image below with the two dots. These double bar repeat signs saved composers the time of having to write out the same thing twice, and help cut back on page turns for musicians.

Sometimes there are sections of music within a piece that are repeated beginning at a particular spot in the music. These sections will be bounded by repeat bar lines on both ends, with one repeat bar line facing to the left and the other facing to the right, sort of like how questions in written Spanish are bounded by question marks: one at the end and the other inverted at the beginning of the question.

How Many Bars Belong?

When I work with students on composition and they ask me about form and length, my first answer is always to follow your ear and write what feels right. Sometimes this is good enough, but I am often pressed to follow up with another slightly more specific morsel of musical wisdom. Most of what we hear, as far as musical form goes, is written in 2’s, 4’s, 8’s, 16’s, 32’s, etc. This is so often the case that any time a phrase is not four or eight bars long, it feels peculiar.  

Music is a cultural construction, of course, so there is no reason it needs to be this way. But until musicians set about making and popularizing new conventions, these symmetrical assortments of bars are what audiences expect. The origin of this convention can be traced to the Classical era, in which balance and symmetry were among the most highly-valued elements of composition.

The antecedent and consequent phrase pairing is a fundamental building block of classical composition. In an antecedent-consequent phrase pairing, also known as a period, the first phrase is something of a question, typically ending in a half-cadence in the dominant key area or some other less conclusive ending, with the second phrase answering that question with a full resolution to the tonic (more conclusive).  

Greensleeves provides an excellent example of a musical period, but there are countless examples that could be found that work just as well. While the period itself is no longer the standard in putting together verses and choruses, the fact that verses are generally made out of phrases of the same length is a vestige of this symmetry- and balance-affirming approach to composition. Thus, if the musical phrase that serves as the indivisible building block of a verse is four bars long, that verse will likely end up 8 or 16 bars long, or perhaps 32, although that might start to feel like a double-verse. Anything else would be a compositional choice that would catch the listener off-guard (which may, of course, be the goal).

Wrapping Up

Whether music is written or performed live, the important thing is invariably to feel it. Feeling the music will get you further than talking or writing about it ever possibly could. That said, being able to communicate with other people about music can be a really helpful skill, so hopefully, this deep dive into the theory behind the bar and how to make sense of it in context will help facilitate your future communications about music.