The standard musical keyboard on a piano contains 88 keys that are each assigned one of seven letters from the English alphabet. These letters are A through G, which--including their "accidental" variations--repeat themselves along the length of the keyboard.

White Keys

Each white key on the standard piano keyboard is designated with one of the following seven letters: A, B, C, D, E, F or G.

Black Keys

The black keys are the accidentals--or sharps and flats--so each one is designated one of the following: A-sharp, C-sharp, D-sharp, F-Sharp, G-sharp, A-flat, B-flat, D-flat, E-flat or G-flat. Notice that some letters are missing; these gaps occur where there are two white keys next to each other.

Layout

Black keys are in groups of twos and threes. Reading from the left, the white keys touching a group of two black keys are C, D and E; the white keys touching a group of three black keys are F, G, A and B.

Accidentals

Each black key has two letter designations depending on whether you reading it as a sharp or a flat of a nearby white key. Reading from the left to right, a group of two black keys is C-sharp/D-flat and D-sharp/F-flat; the group of three black keys is F-sharp/G-flat, G-sharp/A-flat and A-sharp/B-flat.

Musical Notation

The black dots on the lines of music represent letters. Playing music involves finding the letters on a keyboard, playing them in sequence and timing the tempo as noted in the score.

Source:

Lovingkeyboard.com: Musical Keyboard Layout