How to Tune a Guitar Using a Tuning Fork
Once you get good enough at discerning pitches, you will be able to tune the guitar using a single-pitched tuning reference like a tuning fork. If you know how to tune a guitar with a tuning fork or some other fixed source, you can play with other instruments or voices and ensure that everyone is playing by the same tuning rules. Besides, your guitar and strings are built for optimal tone production if you tune to standard pitch.
The tuning fork offers only one pitch, and it usually comes in only one flavor: A (the one above middle C, which vibrates at 440 cycles per second, commonly known as A-440). Luckily, that's really the only note you need. To tune a guitar using a tuning fork:
Strike the fork against something firm, such as a tabletop or kneecap.
Hold it close to your ear or place the stem (or handle) — and not the tines (or fork prongs) — against something that resonates, such as a tabletop or even the top of the guitar.
You can even hold it between your teeth, which leaves your hands free! It really works!
At the same time, play an A note (the open 5th string on your guitar) and tune it to the fork’s tone.
Once you get your your open 5th string (A) in tune with the tuning fork’s A, you can tune every other string to that string by using the fifth-fret relative tuning method.
Using a tuning fork requires a little finesse. The process is kinda like pulling your house keys out of your pocket while you’re loaded down with an armful of groceries. The task may not be easy, but if you do it enough, you eventually become an expert.