The pitch distance between any given two notes can be measured by semitones, or by half-tones. The distance between each 2 neighboring notes equals to 1 semitone, or to half a tone.
For example, the distance between the notes 'C' and 'F' in the following example equals 5 semitones, or 2.5 tones:
Can you tell the distance in semitones between 'C' and 'A'?