E A D G B E
The thickest string is lowest in pitch and the highest in pitch is the thinnest string.
The lowest string is an E string and is number 6, it is the thickest string. The thicker the string the slower the vibration. The highest or thinnest string is string 1 and is also an E string.
The strings are numbered low E6 – A5 – D4 – G3 – B2 – E1 high
Note names correspond to number of vibrations per second. Octaves are equal divisions and for this reason the notes are given the same names. For example:
A – 440 A – 220 A – 110
The numbers are vibrations per second or frequencies or hertz.
The frequency of the low E string is 82.406886 while the frequency of the high E is 329.63 Hertz. Other instruments will tune to the same standard which is A 440, this sometimes varies slightly in different countries. A piano tuner would use references like this to tune the piano. When we use a digital tuner it reads the frequencies or vibrations and translates that to a note name.