A number chart writes a song in scale degrees instead of chord names. The tonic is always 1, so in the key of C the 1 is C and in the key of G it is G, and the chart itself never changes. That is the whole point of it: when the singer wants the song a tone lower, nobody rewrites anything.
It came out of the Jordanaires, a Nashville vocal group doing three or four sessions a day in the late 1950s with only lyrics in front of them. Neal Matthews Jr. worked out the numbering, Charlie McCoy pushed it further, and the session players turned it into the chart system. Chas Williams published the book in 1988.
The seven chords
Number the major scale and you get the chords that live in the key. Three are major, three are minor, and the seventh is diminished and barely ever used. In C:
| Number | In C | Quality |
|---|---|---|
| 1 | C | major |
| 2- | D minor | minor |
| 3- | E minor | minor |
| 4 | F | major |
| 5 | G | major |
| 6- | A minor | minor |
| 7° | B diminished | diminished, and rare |
A bare number is major. A dash after it makes it minor. Those two rules cover most of every chart you will ever see, and a great many songs are nothing but 1, 4 and 5.
Here is the same degree twice. Both diagrams show the 4, and in both the numbers on the dots read the same, because they are counted from the chord. Only the letters underneath change.
Everything else
Chords from outside the key get an accidental in front of the number. Qualities and extensions go after it. This app reads all of the following.
| Written | Means | In C |
|---|---|---|
| ♭7 | flatten the degree | B♭ |
| ♯4 | sharpen the degree | F♯ |
| 5- | minor | G minor |
| 57 | dominant seventh | G7 |
| 4Δ | major seventh | Fmaj7 |
| 2-7 | minor seventh | Dm7 |
| 7° | diminished | Bdim |
| ♯4°7 | diminished seventh | F♯dim7 |
| 1+ | augmented | Caug |
| 5sus | suspended fourth | Gsus4 |
| 1/3 | an inversion, third in the bass | C/E |
| 4/5 | F over a G bass | F/G |
The accidental signs are the real ones, ♭ and ♯, but a plain b and # are read the same way here because they are what a keyboard produces. Convention leans on sharps when a chord is walking up, as in 1 to ♯1°, and flats otherwise.
Minor keys are numbered from the relative major
This is the part that catches people, and the app used to get it wrong. A song in A minor is normally written in the numbers of C, its relative major, so the A minor chord you keep landing on is written 6- rather than 1-. Where a major key song leans on 1, 4 and 5, a minor key song leans on 6-, 2- and 3.
The 3 there is worth a second look. In A minor it is E, and it is usually played major even though the key says it should be minor, because it is doing the job the 5 does in a major key: pulling you home.
You can write it as 1-, 4-, 5 instead, counting from the minor tonic, and this app will read a chart marked that way. It is just that most players reading over your shoulder will expect the first version, so that is what the library uses.
Bars and time
Every bar gets a number, so the chart tells you when to change. Four bars to a line reads easily; eight is common for eight bar phrases, usually with a gap between the fourth and fifth. A twelve bar blues is twelve numbers.
Two chords in one bar is a split bar, written underlined on paper and with both numbers inside the same bar here. If the split is uneven, the rhythm gets written above it. A diamond round a number means let it ring, usually a whole bar. A > or ˇ above a chord is a push: come in an eighth note early. Repeat signs, first and second endings, fermatas and codas all appear on number charts too, because the people who invented the system could read notation perfectly well and only wanted a faster way to write a chart.
Why it is worth learning
Because it is the same idea the fretboard tool is built on. A degree is a relationship rather than a note, and once a song is stored as relationships you can move it anywhere. Learn a chart as 1 4 5 and you have learned it in twelve keys. Learn it as G, C, D and you have learned it in one.