F 6sus4 on Piano, and the Number That Writes It

F 6sus4 spells F – Bb – C – D. That much is fixed. What is not fixed is what it is CALLED: hand the same chord to a chart in A# and it is written 5; hand it to a chart in C and the identical chord is written 4, on a page nobody had to rewrite.

F answers to the 1, 2, 3, 4, 5, 6 and the 7 depending on what got called: it is a plain number in 7 of the twelve keys and needs an accidental in the other 5.

A piano player reads the whole chart at once — the instrument the numbers are usually written at, and the one that can voice a slash bass and the chord above it without asking anybody else to cover half of it. The digit is split between two hands on the same beat: whatever a slash mark puts under it goes to the left, the chord itself to the right, and a bare number leaves the left hand on the root.

Every voicing below is drawn across all 88 keys from A0 to C8 — root position, the 1st, 2nd and 3rd inversions and the two-hand split a slash number asks for — and each one is a diagram rather than a recording, because this site's playback is a plucked-string engine and a piano played through it would be a guess.