Originally posted by noticingthemistake
That's easy, if you know the chromatic scale.

E F F# G Ab A Bb B C C# D Eb E

If you know the names of each string. You just go up the chromatic scale as you go up the frets. So the lowest string open is E, the first fret is F, the second F#, and so on.

It's better if you go through it this way because if you just look at a diagram, you'll forget it. So just practice you chromatics all over the neck, saying each note as you play it. Then you'll know it in a couple of days, and you won't forget it either.