Learn About Measures in Music: Basic Musical Punctuation Guide

In music theory, a measure (or bar) refers to a single unit of time featuring a specific number of beats played at a particular tempo. When writing music on a page, composers break their compositions into measures—digestible sections that help players perform the music as intended. When a piece of music is divided into measures, players need only process a little bit of music at a time, allowing them to remain focused on delivering the best possible performance. Measures are designated by vertical measure lines or bar lines that run perpendicular to the staff.

Measures exist to organize long pieces of music into smaller units. Professional musicians like orchestra members and session players read music in real-time as they perform, and they’re often able to perform a piece of music on their very first attempt. By breaking the music into smaller pieces with bar lines, composers facilitate easy sight-reading and better overall performances.

A musician reads a measure of music from left to right, playing the notes in sequence as they appear. To read a measure of music, you need to understand the basics of tempo, meter, and note values. The information conveyed within a measure of written music depends on the:

• Time signature: Musical time signatures show the number of beats per measure (the top number in a time signature) and the duration of each beat (the bottom number in the time signature). For instance, 3/4 time indicates that there are three beats per measure and each beat has the duration of a quarter note. The most common time signature in Western music is 4/4 or common time.
• Tempo: Tempo refers to the speed of a section of music. It can be indicated in metronome markings using beats per minute (BPM) or by using descriptive words (traditionally Italian words describe tempo like adagio or andante).
• Note values: Individual notes within a measure last for a specific fraction of the duration of that measure. For instance, quarter notes last for one quarter of a 4/4 measure, while eighth notes last for one eighth of that same 4/4 measure.
• Bar lines: Different types of bar lines indicate different player behavior, from continuing onward to repeating a section to stopping the music altogether.

Different types of bar lines appear in sheet music, each type indicating the start or end of a measure and communicating instructions for the player.

1. Single bar line: A single vertical line that indicates the end of one measure and the beginning of another.

2. Double bar line: Two side-by-side vertical lines, indicating the end of one section and the beginning of another.

3. End bar lines: Two vertical lines, the second line thicker than the first. This indicates the end of a musical movement or an entire composition.

4. Start repeat: Double bar lines—the first one thicker than the second—followed by a pair of dots that look like a colon punctuation mark. This indicates the first measure of a repeated section.

5. End repeat: Double bar lines—the second one thicker than the first—preceded by a pair of dots that look like a colon punctuation mark. This indicates the final measure of a repeated section.

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