How to play C7 (C 7) on Piano

C7 is the C 7 chord. It is built from 4 notes — C, E, G and A# — which sit at the root, major third, perfect fifth and minor seventh above the root C. Written as a formula that is 1P – 3M – 5P – 7m. Those intervals, not the note names, are what give the chord its character: move all of them to a different root and you still hear a 7 chord.

On piano, C7 is played as a 4-note voicing. The diagram above highlights every key you press, ascending from the lowest. Because the piano lays the notes out in a straight line, the shape you see is the chord spelled literally — there are no duplicated or omitted notes to reason about, which makes the keyboard the fastest place to hear how the chord is actually built before transferring it to a fretted instrument.

The major third between C and E is what makes this chord sound bright and settled. Flatten that one note by a semitone and you have C minor instead — a single semitone is the whole distance between the two moods. The added minor seventh stops the chord from sounding like a resting place — it leans forward and wants to resolve, which is exactly why it turns up at the end of a phrase rather than the start.

C7 belongs to 1 major key, including F major, where it is the V chord. That is the practical reason to learn it: a chord that is diatonic to several keys turns up constantly, and knowing which degree it occupies tells you what tends to come next. A V chord in F major most often moves toward the tonic, so practising C7 in the context of F will teach you more than practising it in isolation.