A time signature is a set of two numbers, one on top of the other one, written right after the key signature in a piece of music. The two numbers in a time signature tell you how many of one kind of note there are in each measure in the song. For example, [math]\frac 4 4[/math] means that there are four quarter notes, or notes that last one beat, in each measure.
Finding out what certain time signatures mean
The number in the top of the time signature tells a player how many of a certain kind of note there are in each measure. The number in the bottom of the time signature tells what kind of note is used a certain number of times in each measure. The number on the bottom of the time signature can be any number that follows the pattern 1, 2, 4, 8, 16, 32..., where each number in the pattern is two times the number that came before it. So, 64 could be a number that is put in the bottom of the time signature, but 65 could not be one.^{[1]}
Number on the bottom of the time signature

What it means

1

A whole note lasts one beat

2

A half note lasts one beat

4

A quarter note lasts one beat

8

An eighth note lasts one beat

16

A sixteenth note lasts one beat

This table shows different numbers that could be the bottom of a time signature, and what they mean. Note that each note down lasts for onehalf of the amount the note above it lasted. For example, one quarter note lasts one beat, and one half note lasts one half of a beat, because one divided by two is onehalf.
Time signatures that are used very often
Time signature

What it means

[math]\frac 4 4[/math]

Four quarter notes in each measure^{[2]}

[math]\frac 3 4[/math]

Three quarter notes in each measure^{[2]}

[math]\frac 2 4[/math]

Two quarter notes in each measure^{[2]}

[math]\frac 6 8[/math]

Six eight notes in each measure^{[2]}

Symbols that are used instead of time signatures
 The letter C has been used instead of using [math]\frac 4 4[/math] time.
 The symbol "" is called "cut time" and has been used instead of using [math]\frac 2 2[/math] time, where every note is cut in half. So, in "cut time", a quarter note, which usually gets one beat, gets onehalf of a beat.
Other pages
References


 Chords and scales  

 Composition  

 Note groupings  


