There are many methods to tune a guitar. Some use pitch pipes or another instrument to tune the guitar. There are also electronic guitar tuners that do an excellent job of helping you to tune your guitar. But using a tuning fork to tune a guitar is simple and fun. Pulling out a tuning fork at your next gig will probably raise some eyebrows from your friends. It makes you look less like a garage band ax player and more like a concert guitarist.
Tuning forks are pretty simple to find either locally or online. Amazon has the right kind of tuning forks for $7 or less. You can get tuning forks in different pitches, but the easiest to get your hands on is a fork called "A-440." This is the note of A played at 440 Hertz (beats per second). Most instrument tuners will tune relative to the A-440 pitch.
A typical guitar has 6 strings. They are named E-A-D-G-B-E (top to bottom). You see that the 5th string (reading from bottom to top) is named A. It plays the note of A when played in the open position. That A note is vibrating at 110 Hertz, or 2 octaves lower than the tuning fork. The A played on the G string (3rd string, second fret) is A at 220 Hertz, or 1 octave lower than the tuning fork. Finally the A played on the 1st string, fifth fret, is an A at 440 Hertz. Aha! The key to using the tuning fork the easy way. But, first, the conventional way.
Using a Tuning Fork the "Proper Way," a.k.a., the Hard Way
The standard way to use a tuning fork is to strike the fork on something hard that won't be damaged by the fork, nor that will damage the tuning fork. NEVER hit your guitar with the tuning fork! The fork is much harder than your guitar and can easily damage the wood. An ever handy hard surface is your leg or knee. I guess your head is also available, but not recommended. When striking the tuning fork to get it resonating properly, you need to hold it on the single prong, not on the forks. If you touch the forks they will stop vibrating.
After you have the tuning fork vibrating there are a couple of different ways to use it. If you hold the fork up to your ear, you can barely hear the tone. However, if you press the stem, or sometimes they will have a ball, of the tuning fork on your head near your ear, you will be able to hear the tone clearly. I usually press it into the bone just in front of my ear. It is almost eerie the way it produces sound inside your head instead of through the air.
You can also press the stem, or ball, onto the face of the guitar. It will ring clearly.
Either of these methods will give you the sound of the A note at 440 hertz. You can then tune the 5th string to that tone, remembering that it will be 2 octaves lower. You could also tune the 3rd string stopped at the second fret for an A, 1 octave lower. Finally, you can tune the 1st string stopped at the fifth fret to achieve an A at the right octave. Then all other strings can be tuned relative to one of these A notes.
Each of these methods have their flaws. If you don't have a very keen ear, you may have trouble getting the 5th string tuned right because of the 2 octave difference. It is also difficult to tune a string that is stopped at a fret because of various ways of manipulating the string while pressing it down to the fingerboard. But, there is an easier way!
Using a Tuning Fork the Easy Way
After striking the tuning fork on your leg or knee, place the stem onto the first string of your guitar. You want to just touch the string, not press it down. Slide the tuning fork on the string near the fifth fret. When the tuning fork and the string are harmonically balanced you will hear a strong tone from the tuning fork. If you hear that tone directly above the fret then you have achieved a perfect A. If the tone coming from the tuning fork is in front of, or behind the fret, then adjust the tuning machine on the 1st string until the tone sounds strongest immediately above the fifth fret.
Viola! The 1st string is in tune and ready to be used to tune the rest of the strings in a conventional manner. You can also use this technique on the 3rd string above the second fret, or any other A on the guitar that is over a fret and not an open string.
How a Tuning Fork Is Superior to Other Tuning Methods
Using a tuning fork in this simple way eliminates many of the problems with tuning a guitar with other methods. It is also fairly easy to get right in a noisy room.
When tuning off of pitch pipes, a piano, or any other instrument, it is difficult for some people to hear the right note. This is because the color of the tone is different. It may be the exact same note mathematically, but for some people it does not sound the same. I happen to be one of those people.
Using an electronic guitar tuner can be problematic in noisy environments. Using the easy method of tuning with a tuning fork, no other sound can interfere with the fork and string. It is perfect every time.
Now that I have convinced you to buy a $7 tuning fork let me tell you the one negative aspect of using it. As I mentioned, I don't hear tones very well from one instrument to another. Using this method I can dial in a guitar as easily as someone with perfect pitch. But because it is so easy, I am often embarrassed to pull out the tuning fork; essentially announcing to my tonally blessed playing partners that I have inferior auditory equipment compared to them.
BONUS TIP: When tuning a guitar in a noisy room, you can hug the guitar so that you can press your left ear on the shoulder of the instrument. This will give you a clear sound directly from the vibrating notes inside the guitar body to your ear.