There are three ways to tune a bass guitar to itself: the 5th-fret method, the 7th-fret method, or the harmonics method. Knowing how to use the 5th-fret tuning method on a bass guitar is a great tool. This is the most common type of relative tuning and can be used without any reference point required. But eventually all forms of relative tuning come down to this: You tune one string of your bass to a reference pitch, and then you tune the other three strings to that tuned string.
In all cases, if the notes don’t match exactly, you hear a wavering sound. When you turn the tuning head for each string, the wavers occur at wider intervals as they approach an exact match. When you find the exact match, the wavering stops.
Although purely relative tuning is great when you're playing solo, if you’re going to be playing with other people, be sure to get a reference pitch for the E string (the lowest and thickest string) from one of the other tuned instruments before starting.
Using one of the fingers on your left hand, press the E string down at the 5th fret.
Be careful not to touch the A string because it needs to vibrate freely. The place to press is actually between the 4th and 5th frets, slightly behind the 5th fret.
Strike the E and the A strings together with your right hand and let them ring.
While you’re comparing the sounds of the two strings, keep your left-hand finger at the 5th fret of the E string. Listen to whether the A string is lower (flat) or higher (sharp) than the E string. The notes should be a perfect match. You'll hear a wavering sound if the strings aren’t in tune.
Turn the tuning head for the A string accordingly until the strings are in tune with each other.
Get used to turning your tuning heads with your right hand (by reaching over your left hand) when using this method.
Press the A string down at the 5th fret.
Make sure that you only touch the A string.
Strike the A and open D strings together and let them ring.
Turn the tuning head for the D string until the pitch of both strings matches perfectly.
Press the D string down at the 5th fret.
Strike the D and open G strings together and let them ring.
Adjust the tuning head for the G string until the pitch of the fifth fret of the D string matches the open G string perfectly.