Locate middle C on the piano or keyboard you are tuning the guitar from. If you don't know where middle C is, you can find it by looking at the black keys or by counting from left to right. The C key is always the white key located directly to the left of two grouped smaller black keys. On an 88-key piano or keyboard, middle C is the fourth C to the right (the 24th white key). On a 49-, 61-, or 76-key piano, middle C is the third C to the right (the 15th white key).
Identify the bottom E string of the guitar. This is the sixth string on the guitar, located on the right of the guitar when the instrument is facing you. You will want to tune this string to the first E to the right of middle C on the piano. The E key is the second white key to the right of middle C. Tune the sixth string of the guitar to the E key of the piano. Strike the E key and then turn the tuning peg for the sixth string, plucking the string until the two sounds match as closely as possible.
Move to the fifth string, the B string. This will be located to the left of the sixth string when the guitar is facing you. This string should be tuned to the B key, which is the white key directly to the left of middle C on the piano. Strike the B key and then turn the tuning peg for the B string, plucking the string until the two sounds match as closely as possible.
Tune the fourth string of the guitar, the G string, to the first G key to the left of middle C on the piano. The G key is the third white key to the left of middle C. Strike the G key and then turn the tuning peg for the G string, plucking the string until the two sounds match as closely as possible.
Tune the third string of the guitar, the D string, to the first D key to the left of middle C on the piano. The D key is the sixth white key to the left of middle C. Strike the D key and then turn the tuning peg for the D string, plucking the string until the two sounds match as closely as possible.
Tune the second string of the guitar, the A string, to the second A key to the left of middle C on the piano. The second A key is the ninth white key to the left of middle C. Strike the A key and then turn the tuning peg for the A string, plucking the string until the two sounds match as closely as possible.
Tune the first string of the guitar, the top E string, to the second E key to the left of middle C on the piano. The second E key is the 12th white key to the left of middle C. Strike the E key and then turn the tuning peg for the E string, plucking the string until the two sounds match as closely as possible.