How To Transpose Guitar Chords

Knowing how to transpose guitar chords from one key to another can come in very handy under certain circumstances.
Let's say for instance that you have just learned how to play a new song on your guitar. Perhaps you've spent hours getting the chords down and now you're really excited about playing it for some of your friends.
But then something unexpected happens when you try to sing the melody. To your dismay you discover that the tune is either too high or too low for your voice range. What do you do now?
The answer is easy- you simply transpose it to another key! But, of course, you will need to understand a few basic music concepts before you can do this.
The first thing you will need to realize is that every song is written in a key, and there are twelve keys in music. Each key is derived from a specific scale that bears the same name.
For example, if a song is written in the key of C, all the chords and notes of the song will come from the C major scale. So, in order to transpose a song from the key of C to the key of G you would need to know how each chord relates to it's particular scale. This can be done by using a simple numbering system.
There are seven letters which identify each of the seven tones (or degrees) of a major scale. Seven Roman Numerals are commonly used to identify the chords that relate to each degree of a scale. Here is an example of how this is done using the notes of the C major scale: