There are a couple shortcuts one can take to determine the key of a peice based on how many sharps or flats there are in a given key signature.
If the key signature is composed of sharps, then one can determine the key based on the position of the last sharp (the rightmost sharp).
Using the solfege scale (Do, Re, Mi, etc... --think "Sound of Music") The Key of the song will be on Do. i.e, if a song is in the key of C, then Do will be on C. Key of G, do will be on G.
In a key signature composed of sharps, the last sharp will be on Ti, which is one note below Do. So, if the last sharp is an F#, then the key will be G. If the last sharp is a C#, then the key will be D. If the last sharp is a G#, then the key will be A. if the last sharp is a D#, then the Key will be E.
If a key signature is composed of flats, one can determine the key based on the position of the second to last flat. One can find this by first finding the last flat (the rightmost flat) and then finding the flat imediately previous. The second to last flat will be the key.
If there are two flats, then the last flat will be Eb, the flat previous to the last will be Bb. The song will be in the key of Bb. If there are three flats. The last flat is Ab, the second to last is Eb, the Key is Eb. Four flats, last flat is Db, second to last is Ab. The key is Ab.
If there is one flat. The song is in the key of F.
If there are no sharps or flats, the song is in the key of C.
This is the easy method to determine a key signature.
One can also use a chart called the Circle of Fifths. One can find this by typing "Circle of Fifths" into an internet search engine.
Starting at the Key of C, every sharp moves the key up a fifth, every flat moves the key down a fifth.
If there is one sharp, the key will be one fifth above C, which is the Key of G. A second sharp will move the key up one fifth from G, which is the Key of D.
If there is one flat, the hey will be one fifth below C, which is the key of F. A second flat will move the key one fifth below F, which is the Key of Bb.
Please Note, these methods are for finding MAJOR keys. Another popular scale is the MINOR scale.
Each key signature will have a major and minor scale. Keys are frequently named by their major scale. i.e., the key of F, refers to an F major scale.
To find a minor key, first find it's correspinding major key.
If there are no flats or sharps, then one knows that the Key is C Major. To find the correspinding minor key of C Major, count three half- steps down from C. Three half-steps down from C is the note A. If there are no sharps or flats, then the Key is either C Major or a minor.
Minor chords and keys are frequently notated with a lowercase letter, while major chords and keys are frequently notated by an Uppercase letter.
If there is one sharp, one knows that the key is G Major. Three half-steps down from G is E. So the key is either G Major or e minor.
One flat is the key of F Major. Three half-steps down from F is D. So the key is either F Major or d minor.
The major scale, and minor scale are the two most popular scales. So a song will usually either be in a major or minor key.
To determine whether the key of a song is major or minor, one must analyze the tonal center of the song. If the song seems to resovle to a minor chord, then it is mostly likely in a minor key.
If the song seems to resolve to a major chord, then the song is most likely in a major key.
In a three-note major chord, the first interval will be a Major 3rd. The second interval will be a minor 3rd.
In a three-note minor chord, the first interval will be a minor 3rd, and the second interval will be a Major 3rd.
Another users answer (just in case you wanted a simple answer): If you need to know keys when looking at a key signature, then try researching into the "Circle of Fifths" its easier to do your own research on this, but it's basically a way of remembering your keys in a simple way. Link to image will be pasted below, hope this adds onto the help!
http://www.Google.co.UK/imgres?imgurl=http://www.piano-lessons-central.com/wp-content/uploads/2009/08/circle-of-fifths.gif&imgrefurl=http://www.piano-lessons-central.com/music-notation/circle-of-fifths/&h=502&w=500&sz=20&tbnid=OuWBk8SBOnREgM:&tbnh=225&tbnw=224&prev=/search%3Fq%3Dcircle%2Bof%2Bfifths%2Bchart%26tbm%3Disch%26tbo%3Du&zoom=1&q=circle+of+fifths+chart&usg=__BHmfa2R7VBJBEvL72eDmN-MDlgY=&sa=X&ei=6BCeTbOjNoyZhQeXlfmyBA&ved=0CBsQ9QEwAA
Go up a half-step from the last sharp in the key signature.
The key signature indicates which notes are sharp, natural, or flat. Every key has a specific signature.
It comes before the time signature. The clef comes before the key signature.
D major has a key signature of F sharp and C sharp D minor has a key signature of B flat
There are no sharps or flats in the key signature of C Major.
To find the key signature with sharps, look at the last sharp in the key signature and go up one half step. This note is the key of the music piece.
To find the key signature of "do" in music, look at the last sharp in the key signature. The note one half step above that sharp is "do."
Go up a half-step from the last sharp in the key signature.
To find the key signature of a musical piece, look at the sharps or flats at the beginning of the staff. The number and placement of these symbols indicate the key of the piece.
To find the key signature of a musical piece, look at the sharps or flats listed at the beginning of the staff. The number and placement of these symbols indicate the key of the piece.
A minor has no key signature.
A key signature, accidentals, a piece of music.
To change the key signature in Noteflight, click on the "Key Signature" button in the toolbar and select the desired key signature from the dropdown menu.
The key signature with 7 flats is the key of C-flat major.
All songs have a key signature.
The key with 5 sharps in its key signature is the key of B major.
The key with five sharps in its key signature is the key of B major.