Time Signatures Explained: Simple, Compound and Beyond

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A time signature has two numbers. The top number is the count of beats in each bar, and the bottom number names the note value that counts as one unit. In 3/4 a bar holds three quarter-note beats. In 6/8 it holds six eighth-note units, which listeners usually feel as two beats of a dotted quarter. Simple meters divide each beat in two, and compound meters divide it in three.

#The top number counts beats and the bottom number names the unit

The bottom number is almost always 2, 4 or 8, with 16 appearing in some modern scores. A 4 makes the quarter note the unit, an 8 makes the eighth note the unit, and a 2 makes the half note the unit. So 3/4 reads as “three quarters to a bar” and 6/8 reads as “six eighths to a bar”. Both bars last the same length, the equivalent of three quarter notes, which is why the two are easy to confuse on paper. They differ in how the beats are grouped, and the grouping is what you hear.

The “felt beat” column is the pulse you tap. In the compound signatures the bottom number is still 8, because the notes are written in eighths, but the beat itself is the dotted quarter that spans three of them.

Two symbols stand in for common signatures. The letter C at the start of a staff means 4/4, which is common time. A C with a vertical stroke through it means cut time, 2/2, in which the half note carries the beat. The two describe the same music at different notational speeds: a passage in 2/2 with the half note at 60 sounds the same as one in 4/4 with the quarter note at 120. Composers often choose cut time for a fast piece, so that the notation shows two larger beats per bar in place of four smaller ones.

The top number does most of the structural work. Here is a loop of four chords in C, C major, F major, G major and C major again, written as one chord per beat at 96 beats per minute:

Four beats make one bar of 4/4, so the loop returns to the start of the bar every time. The same four chords in 3/4 do not fit a bar at all. The loop needs 12 beats to come back to beat one, which is four bars of three, so a waltz has to repeat the four-chord figure three times before it lines up with the bar lines.

#Simple and compound meters differ in how each beat divides

In simple meter each beat divides into two equal parts, and the natural count is “one and two and three and four and”. The signatures 2/4, 3/4 and 4/4 are simple: the beat is a quarter note, and each quarter holds two eighths. They differ only in how many beats a bar contains.

Compound meter divides each beat into three. In 6/8 the bar holds six eighths, grouped into two sets of three. The felt beat is the dotted quarter, and the count is “one la li, two la li”. The notation uses eighths because the eighth is the unit, but the pulse you tap is the dotted quarter. Nine eighths and twelve eighths work the same way, with three and four felt beats in the bar. Here are two bars of 6/8 with each dotted quarter written as one felt beat, so each bar holds two beats:

The quickest test is to count. Say “one and two and” over the passage. If the notes sit comfortably in that count, the meter is simple. If each beat seems to want three syllables, the meter is compound. A piece in 6/8 usually sounds like a dance in two with a lilt, while 3/4 usually sounds like a waltz with three distinct steps. Those are tendencies, not rules, and the grouping of the notes is the evidence that settles the question.

#Strong and weak beats follow the grouping

Each meter has a default accent pattern. In 4/4 the first beat is the strongest, the third is a secondary accent, and the second and fourth are weak. In 3/4 the first beat is strong and the other two are weak, which gives a waltz its lean. In 2/4 the strong and weak beats alternate in the simplest possible way, which is why the meter suits a march. In 6/8 the strong pulses fall on the first and fourth eighth notes of the bar, which are the starts of the two dotted-quarter beats, and the other eighths are weaker.

The player does not add any accent, so the accent has to come from your count. This six-chord progression is two bars of 3/4 at 96 beats per minute, with one chord to each beat:

The chords are C, F, G, C, G, C. Count them in threes, and the first chord of each group lands on the strong beat: C F G in the first bar, then C G C in the second. Count the same six chords in fours and two chords are left over at the end, so the phrase does not close on a bar line. The chords have not changed. Only the grouping has.

#Counting along shows where bars close

Here is a C major scale, eight events at 72 beats per minute. The player spaces each event by one beat, so this line counts beats, not note values:

Eight beats fill two bars of 4/4 exactly, and the scale starts on the first beat of each bar. In 3/4 the same eight beats fill two bars and leave two beats over, so the scale stops partway through a third bar. Counting the scale in both meters at the same tempo makes the difference concrete. The same eight beats close a phrase in one meter and leave a remainder in the other.

Try the scale at a faster setting and then a slower one. The count does not change, only the pace. At 72 beats per minute each event lasts about 0.83 seconds, slow enough to count every note. At 144 the same eight events take half as long, and counting in fours starts to feel like a single gesture.

#Where the signature misleads people

The signature does not set the tempo, and it does not fix the felt beat. In 6/8 at a fast tempo the dotted quarter is the pulse, and the bar feels like two beats. At a slow tempo, such as a slow blues or a ballad, a listener may feel the six eighth notes as six separate beats. The notation is identical in both cases. The tempo decides which reading comes naturally, which is why the metronome marking matters as much as the signature.

Two other confusions are common. A bar of 3/8 holds three eighth notes, a simple meter with one beat per eighth, and it lasts half as long as a bar of 6/8, so the two are not interchangeable. The reverse trap is that 2/2 and 4/4 can carry the same music written with half the note values, so the signature alone does not tell you the speed. Ask what the felt beat is before you ask what the signature says.

Not every meter is simple or compound. Five and seven group as 2+3 or 3+2, and those odd groupings are covered in odd meters. The simple-or-compound question asks only how the beat divides.

#What to do with it

Choose a folk tune or a hymn you know well. Clap it twice. The first time, mark the first beat of each bar in 3/4. The second time, mark the two dotted-quarter pulses in 6/8. Use a metronome set to 60, then to 120. At 60 the 6/8 version may feel like six slow counts, and at 120 it should feel like two quick ones. Note which reading you naturally chose at each tempo.

Then write the same tune out in both signatures on paper. The notes will be identical, and the bar lines will move. That movement is the whole difference. The next step is to learn how note values fill a beat, which is the subject of note values, rests, ties and dots, and the compound-meter comparison shows how the same six units can be heard two different ways.

Questions

What does the top number of a time signature mean?

It is the number of beats in each bar. In 3/4 a bar holds three beats. The bottom number names the note value that counts as one unit, so 3/4 means three quarter-note beats and 6/8 means six eighth-note units.

What is the difference between 3/4 and 6/8?

Both bars last the same length, equal to six eighth notes. 3/4 is simple: three beats, each split into two eighths. 6/8 is compound: two felt beats, each a dotted quarter split into three eighths. The grouping is what you hear.

How can I tell compound time from simple time by ear?

Count along with the pulse. If each beat divides into two, the count is "one and two and". If each beat divides into three, the count is "one la li, two la li". Compound meters also tend to lilt rather than march.