G string — G4 in standard tuning
The top string is usually a high G, which gives ukulele its bright, close-position sound. Low-G players replace it with G3, one octave lower.
C string — C4
The C string is the lowest-pitched string in standard high-G tuning. It is also the thickest of the four standard strings.
E string — E4
The E string sits between C and A in pitch and is used in many familiar beginner melodies.
A string — A4
The bottom string is A at 440 Hz—the same pitch commonly used as an orchestral tuning reference.