In this lesson
Bar lines divide written music into bars, also called measures. A time signature tells you how note values are organised within those bars. To read it, you need both the total written duration and the way the beats are grouped.
Bar lines and measures
A bar line is a vertical line across the staff. It marks a boundary between bars.
In a complete bar, the notes and rests in each rhythmic part add up to the duration set by the time signature. A bar of 4/4 might contain four quarter notes, two half notes, or a half note followed by two quarter-note rests.
Count simultaneous notes in a chord as one event with that duration. A chord of three quarter notes played together occupies one quarter-note beat.
A pickup, also called an anacrusis, is an incomplete opening bar. It is one reason you should not assume that every visible bar is full.
Reading the two numbers
Time signatures usually show two numbers, one above the other. In plain text, we write them as 4/4 or 6/8.
The bottom number identifies a note value: 2 means half note, 4 means quarter note, and 8 means eighth note. The top number tells you how many of those values make up a complete bar. These values may be individual beats or divisions of a larger beat.
For example, 4/4 contains the equivalent of four quarter notes; 6/8 contains the equivalent of six eighth notes. The time signature does not require every note in the bar to have that value.
Simple metre
In simple metre, each main beat normally divides into two equal parts. For these common signatures, the top number counts the beats and the bottom number gives the beat value.
| Time signature | Main beats per bar | Usual beat value |
|---|---|---|
| 2/4 | 2 | Quarter note (crotchet) |
| 3/4 | 3 | Quarter note (crotchet) |
| 4/4 | 4 | Quarter note (crotchet) |
| 2/2 | 2 | Half note (minim) |
In 3/4, count “1 and 2 and 3 and” for a bar of eighth notes. Each numbered beat divides into two eighths.
The C symbol for common time means 4/4. A C with a vertical stroke through it means 2/2, also called cut time or alla breve.
Compound metre and 6/8
In compound metre, each main beat normally divides into three equal parts. The top number counts these smaller divisions.
A complete bar of 6/8 has six eighth-note divisions, usually grouped as 3 + 3. That gives two main beats, each lasting a dotted quarter note. A dot adds half the original note value, so a dotted quarter equals three eighths.
Count “1-and-a 2-and-a”, with the six syllables evenly spaced. The numbers mark the two main beats. Counting all six eighths as “1 2 3 4 5 6” can help when practising slowly, while keeping the grouping into two sets of three.
| Compound signature | Main beats per bar | Usual beat value |
|---|---|---|
| 6/8 | 2 | Dotted quarter note |
| 9/8 | 3 | Dotted quarter note |
| 12/8 | 4 | Dotted quarter note |
| 6/4 | 2 | Dotted half note |
In 6/4, the bar totals six quarter notes. A common grouping is 3 + 3 quarters, producing two dotted-half-note beats. Music can use other groupings or a different pulse, so follow the score’s beaming, accents and tempo marking.
Why 3/4 and 6/8 differ
Both signatures contain six eighth-note values in a complete bar. Their usual grouping differs:
- 3/4 has three quarter-note beats: 2 + 2 + 2 eighths.
- 6/8 has two dotted-quarter-note beats: 3 + 3 eighths.
A time signature describes this organisation. The tempo tells you how quickly the specified note unit passes, so 6/8 alone does not tell you a speed in seconds.
To check a rhythm, first add its notes and rests using a common unit, such as eighth notes. Then check how those values group around the main beats.
Further reading
The Open University’s guides to simple time signatures and compound time explain the distinction. Open Music Theory’s compound-metre guide gives further examples.