Bass guitar tuning
Most bass guitars have four strings, which are tuned one octave lower than the lowest pitched four strings of an electric guitar. Thus, the bass guitar's standard tuning is E, A, D, G (lowest to highest string.) 
Note: These frequencies are within both the 12-tone Equal temperament tuning method, and using the A440 (pitch standard). If one simply tunes their bass or other guitar in perfect 5ths, that's actually Pythagorean tuning and will render a flat octave, so you're encouraged to match each open string on the bass guitar to these pitches as precisely as possible. Read more about bass guitar intonation methods, so that your open string or 12th-fret harmonic and fretted 12th-fret frequency do not differ.
|4 String||5 String||5 String
A popular altered tuning is Drop D, which decreases the E string by a whole step downward. This provides a low D, which is desirable for songs in the key of D or G.
- Frequencies, Contrabass Mania, retrieved 2010-08-23