Tones, Semitones & Your First Key Signatures
The smallest distance in Western music, the whole tone it takes two of to make, and how that building block explains your first key signatures.
Explainer
A semitone is the smallest distance between two notes in Western music — on a piano, any two neighbouring keys, black or white, are a semitone apart.
A tone (or whole tone) is simply two semitones put together — the gap from C to D, for example.
A key signature is a set of sharps or flats written right after the clef, telling you which notes are consistently raised or lowered throughout the piece.
C major has no sharps or flats. G major has one sharp (F♯). F major has one flat (B♭) — each because of exactly where the tones and semitones need to fall to keep the scale sounding right.
Worked examples
A semitone
The smallest step of all — any two neighbouring piano keys, such as E to F.
A tone (two semitones)
C to D is a tone — two semitones stacked together.
G major — one sharp (F♯)
Every F becomes F♯.
F major — one flat (B♭)
Every B becomes B♭.