Standard guitar tuning: E A D G B E notes and Hz

In standard tuning the six strings, from the thickest to the thinnest, are E A D G B E.

Notes and frequencies

Frequencies are equal temperament with A4 = 440 Hz, rounded to two decimals.

Tune in a quiet place and play one open string at a time; let it ring rather than plucking repeatedly.
A chromatic tuner shows the nearest note and how far off it is in cents (hundredths of a semitone). Find the note in the table above for that string.
If the note is too low (flat), tighten the string slowly. If it is too high (sharp), loosen it a little below the target and then tighten up to it: approaching from below keeps the string from slipping.
Go through every string, then check them all once more: tuning one string changes the tension on the guitar neck a little.
The Sowlea App’s tuner is free; it marks a string as in tune when it stays within ±2 cents. This website itself has no microphone tuner.

Tune string 6 with a tuner or a reference note first. In each pair below, leave the fretted string alone and turn the peg of the open string until the two match.
Press string 6 at fret 5 and play it together with open string 5: both should be A and sound as one steady note.
Repeat with string 5 fret 5 against open string 4 (D), and string 4 fret 5 against open string 3 (G).
Use string 3 fret 4 against open string 2 (B): this is the one pair that uses fret 4.
Finish with string 2 fret 5 against open string 1 (E). A slow “wah-wah” beating means the two notes are still slightly apart.

Lower string 6 by a whole step from E2 to D2 (73.42 Hz). Check it by ear: open string 6 and open string 4 are now both D, exactly one octave apart.