Measures and Time Signatures

Music moves in time, and that time is organised into small, repeating chunks. This lesson is about how those chunks work: the measure (or bar) and the time signature that tells you how to count it.

Measures and bar lines

A steady pulse of beats is grouped into equal packages called measures. On the page, each measure is separated from the next by a vertical bar line. Grouping beats this way gives music its shape: instead of an endless stream of clicks, you feel repeating cycles of, say, three or four beats.

The first beat of every measure is the downbeat, and it is naturally strong or accented. Your ear uses that recurring accent to sense where each measure begins.

Reading the time signature

At the very start of a piece, just after the clef, you see two stacked numbers. That is the time signature, and each number has a job:

• The top number tells you how many beats are in each measure.
• The bottom number tells you which note value counts as one beat: 4 means a quarter note, 8 means an eighth note, and 2 means a half note.

So 4/4 means four quarter-note beats per measure. It is by far the most common, so common that it is nicknamed common time. 3/4 gives three quarter-note beats, the lilting count of a waltz (ONE two three, ONE two three). 2/4 gives two beats per bar, a crisp march-like feel.

When the bottom number changes

6/8 counts six eighth notes per measure, but you rarely count all six evenly. Instead the eighths group into two sets of three, so the bar is felt in two with a rolling, swaying lilt. This is why the bottom number matters as much as the top: it sets the pace of the beat itself.

Set the metronome below to hear this for yourself. Change the beats per bar to 4, then 3, then 2, and listen for the louder accent that lands on the first beat of every cycle.

The time signature is a promise about counting: how many beats you get, and what a beat is worth. Once you can feel the accented downbeat, you can find your place in any piece of music.