Time Signatures in Music Notation

Notational Convention for Beat Values

popular time signatures
Commonly seen time signatures. © Sidney Llyn

In music notation, a time signature expresses the meter of the music throughout the piece by indicating how many beats are in each measure of music and what the value of each beat is. The time signature can also be called a meter signature or measure signature. In music's common languages it is called the indicazione di misura or segno mensurale in Italian, the signature rythmique or indication de la mesure in French and in German it's referred to as the Taktangabe or Taktzeichen.

The time signature resembles a large fraction and is placed at the beginning of the musical staff. It comes after the clef and the key signature. Both the top number and the bottom number of the time signature maintain unique indications of how the music is measured throughout the piece.

The Meaning of the Top and Bottom Numbers

  • The top number indicates how many beats are in a measure. This can be any number, but it is most commonly between 2 and 12. For example, if the top number is a 4, then there will be 4 beats in the measures. If the top number is a 6, there will be 6 beats in the measure. 
  • The bottom number tells what the length of the beat is. A 4 indicates a quarter note and an 8 would mean an eighth note. So if the top number is a 4 and the bottom number is also a 4 the time signature 4/4 is created. This means there are four quarter-note beats in each measure. Whereas if there was a 6 on top and an 8 on the bottom the time signature created would then be 6/8, meaning there are six eighth notes in each measure. 
  • An exception to the rule of a top and bottom number is when a piece is written in common time or cut time. Common time closely resembles a "C" and has a meter that is the same as the 4/4 time signature, whereas cut time is demonstrated as a C with a vertical line cut through it.

Rules of the Time Signature

There are a few rules to properly notating the time signature on the music staff. 

  1. In most sheet music, the time signature only needs to appear on the very first staff of the composition. Unlike the key signature, which is written on every line of music, the time signature is indicated only once at the beginning of a piece.
  2. The time signature is notated after the clef and the key signature. If a song doesn't have a key signature (for example, if it's in C Major with no sharps or flats), the time signature is placed directly after the clef.
  3. If a change in meter takes place during the song, the new time signature is first written at the end of the staff above it (after the last bar line), and then repeated at the beginning of the staff it affects. Similar to the initial time signature, it is not repeated on every line after this.
  4. A change of meter occuring mid-line is preceded by a double barline; if the change is mid-measure, a dotted double barline is used.

The speed of a song is specified by its tempo, which is measured in beats per minute (BPM).