Time Signatures

Look at the very start of a piece, after the clef and any sharps or flats. You will often see two numbers stacked one on top of the other, like a little fraction with no line between them. That stack is the time signature.

It is there to organize the beats. Music runs in repeating groups, and the time signature tells you how the beats are packed into each group. Once you know it, you know how to count the music that follows, until a new time signature appears.

Find a piece of sheet music and look after the clef, and after any sharps or flats, for two stacked numbers. Those two numbers are about to tell you how to count.

A time signature is the metric contract for a piece: two stacked numbers, placed after the clef and key signature, that fix how beats are grouped and what counts as a beat. Every rhythm in the piece is read against it.

It works by declaring a repeating unit, the measure, and setting its size. Music runs in equal groups, and the time signature is where that grouping gets stated. Everything that follows is poured into the frame it sets.

The two numbers do different jobs. Take the top one first. It tells you how many beats are in each measure.

A measure (also called a bar) is one group of beats, marked off by thin vertical bar lines across the staff. If the top number is four, every measure holds four beats: count "one, two, three, four," reach a bar line, and start over at one. If it is three, you count "one, two, three" per measure, like a waltz.

Tap four even beats, say "bar line," and tap four more. Now you are feeling a top number of four.

In simple meters the top number counts the beats in each measure, and before a single note value is chosen, it has already set the meter's character. A three on top carries the lilt of a waltz; a four gives the square evenness of much popular and classical music; a two drives the tighter pulse of a march. The number of beats in a group is musical information all by itself, and a listener feels it long before they could name it.

That is why the same tune feels different in three than it does in four. The grouping does expressive work, right there in the top number, before any melody arrives.

Now the bottom number. It tells you which note gets one beat, using a simple code: the number stands for a note value.

A four on the bottom means the quarter note gets one beat, and that is the most common one. An eight means the eighth note gets the beat, and a two means the half note does. So the number is pointing at a single note and saying, this one is worth one count.

Set a pulse and clap one quarter note on each beat. Each clap is a quarter note lasting one beat, and that is exactly what a bottom number of four tells you.

That lower number is a denominator in the literal sense: a 4 means quarter notes because a quarter note is one-fourth of a whole note. Read it as the fraction the whole note is being divided into to make one beat (in compound meters, one division of the beat, as Part 5 explains), and the 8 or the 2 falls out of the same reasoning.

Seen that way, the choice is a matter of notation. Writing a passage with the eighth note as the beat rather than the quarter leaves the sound identical but changes how the rhythms are notated and beamed, which is exactly why one piece of music can appear under more than one time signature.

Put the two numbers together and you can read a bar. Take four-four: four beats per measure, quarter note gets the beat. It has a nickname, common time, and a symbol shaped like a big C often stands in for it.

In four-four, the notes and rests in each full measure add up to four beats. A whole note fills a measure by itself. Two half notes fill it. Four quarters fill it. A half note plus two quarters fills it too. As long as it totals four, the measure is complete.

Count "one, two, three, four" and clap a bar of four quarter notes. You have just read one measure of common time.

Common time, four-four, is the meter of a great deal of Western music: four quarter-note beats to a bar. Reading in it takes the bar counting from the rhythm class and fixes the size of every bar.

That is the shift a time signature brings. In the rhythm class you added durations until they filled a bar; here the meter sets each full bar at four beats, and it recurs, bar after identical bar, as a steady grid. Fixing the group size is what turns a stream of durations into music you can read, rehearse, and keep your place in.

Time signatures come in families. Some, like two-four, three-four, and four-four, count plain beats (one, two; one, two, three; one, two, three, four), and each of those beats splits into two. These are the ones you will see most.

Others split each beat into three. Six-eight is a common one: six eighth notes in a measure, usually felt as two big swaying beats that each split into three. Here the 6 and the 8 count the eighth notes, not the big beats you feel.

There are shorthands too. A C-shaped symbol means four-four, and the same symbol with a slash through it means cut time, two half-note beats a measure.

The families split on what the beat itself is made of. In simple meters the beat is a plain note that halves into two; in compound meters, with six, nine, or twelve on top, the beat is a dotted note that divides into three, which is why six-eight reads as two dotted-quarter beats, each holding three eighths. So in a compound meter the numbers name the division rather than the beat: the 6 and the 8 count eighths, and at slow tempos players often count all six.

The two common symbols are historical leftovers. The C for common time is a broken circle inherited from medieval mensural notation, a mark whose meaning has nothing to do with the word "common," and cut time is its slashed form, halving the reference toward a two-two feel. Learn the families and those two marks and you can name and count most meters you meet.