Whole steps and half steps – free music theory course

All Western music is built on one unit of measurement: the semitone (or half step), the distance between two immediately adjacent piano keys, black or white. Two semitones make a tone (or whole step).

C → C♯: a half step (next key).
C → D: a whole step (you "skip" the black key C♯).
E → F and B → C: only a half step, because there is no black key between them!

Listen to these two "natural" half steps, E-F and B-C: they are the only places on the keyboard where two white keys are direct neighbours. This irregularity gives the C major scale its particular shape: whole, whole, half, whole, whole, whole, half.

M:4/4
L:1/4
Q:1/4=80
K:C
C D E F | G A B c |]
w: W W H W W W H

Diatonic and chromatic semitones

Theory distinguishes two kinds of half step, which sound the same on the piano but are spelled differently:

chromatic semitone: same letter, different accidental (C → C♯, E♭ → E);
diatonic semitone: two adjacent letters (C → D♭, E → F, B → C).

M:4/4
L:1/4
K:C
C2 ^C2 | C2 _D2 | E2 F2 | B2 c2 |]

Count without mistakes: put a finger on the first note and move key by key, black keys included, counting "1, 2, 3…" for each key you land on. The number of moves = the number of half steps. Don't count the starting key!

Common mistake: thinking there is always a whole step between two white keys. E-F and B-C are the exceptions — the source of 90% of beginners' scale mistakes.