Duration of Notes
The top number in a time signature tells you how many beats are in a measure. The bottom number indicates the type of note that receives one beat. Therefore, in the following time signature,
(“four-four”)
the 4 on the bottom indicates that a quarter note receives one beat. The top number tells you that there are four quarter notes in a measure.
Common Time
Because of its frequency of use, is referred to as “common time” and is sometimes represented by the symbol 
.
Looking back at our note relation chart, we can see that in 4/4 time, a whole note receives 4 beats, a half note is held for 2 beats, a quarter note 1 beat, an eighth note receives half of one beat, and a sixteenth note receives a quarter of one beat.
Note that if the bottom number of the time signature changes, all these values change as well. It is the relationship between the notes that does not change.
In the chart below, select the type of note that should receive one beat. The second column will show the number of beats each type of note receives based on your selection. The final column shows you what the bottom number of the time signature will be. Click on each of the different types of notes, and observe how the values change.