Nashville Number System

A shorthand for chord charts that works in any key. Each chord is written as the scale degree of the key (1 through 7) with optional marks for quality, rhythm, and bass note. Change keys and the chart still reads the same — only the players retune their fingers.

What it is

The Nashville Number System (NNS) was developed by session musicians in 1950s Nashville so a chart could be transposed instantly when a singer changed keys. Instead of writing chord names like G C D, you write the scale degree the chord is built on:

1 = chord built on the first scale degree (the tonic)
4 = chord built on the fourth scale degree (the subdominant)
5 = chord built on the fifth scale degree (the dominant)

In the key of G major, 1 4 5 is G–C–D. In the key of C major it is C–F–G. The numbers stay; the letters change.

NNS numbers vs. Roman numerals

Classical theory uses upper- and lowercase Roman numerals (I, ii, iii, IV, V, vi, vii°) where the case carries the chord quality. NNS uses Arabic numbers and writes the quality as a separate mark, so a working chart stays fast to read on the bandstand.

Diatonic chords in the major scale, Roman numerals vs. NNS, examples in C and G
Degree	Roman	NNS	Quality	In C major	In G major
1	I	1	major	C	G
2	ii	2−	minor	Dm	Am
3	iii	3−	minor	Em	Bm
4	IV	4	major	F	C
5	V	5	major	G	D
6	vi	6−	minor	Am	Em
7	vii°	7°	diminished	B°	F#°

The default for a bare number is a major triad. A minor chord gets a minus sign or a lowercase m; diminished is a small circle; augmented is a plus sign.

Chord-quality marks

Chord-quality marks used in the Nashville Number System
Symbol	Meaning	Example
4	major triad	4 = IV (e.g. F in C major)
4− or 4m	minor triad	4− = iv (Fm in C major)
4°	diminished triad	7° = vii° (B° in C major)
4+	augmented triad	5+ over a tonic pedal
4⁷	dominant 7 (b7 added)	5⁷ = G7 in C major
4Δ or 4M7	major 7	1Δ = Cmaj7 in C major
4−⁷	minor 7	2−⁷ = Dm7 in C major
4sus	suspended (sus4 by default)	5sus = Gsus4 in C major
4/3	slash chord — 4 chord with 3 in the bass	1/5 = C/G in C major

Extensions stack just like in lead-sheet notation: 1⁹, 5¹³, 2−¹¹. Alterations such as b5, #9, b13 are written in parentheses after the number, e.g. 5⁷(b9).

Chromatic / non-diatonic chords

Chords that fall outside the diatonic 1–7 use flat or sharp in front of the number to show how the root is altered relative to the major-scale degree.

b3, b6, b7 — borrowed from the parallel minor (e.g. b7 = Bb in C major).
#4, #5 — chromatic passing chords or secondary leading tones.
5/4 — read as “5 of 4”, a secondary dominant: the dominant chord of the 4 chord. In C major, 5/4 is C7 (the V of F).

The slash form X/Y is overloaded: with simple numbers it means a slash chord (top number is the chord, bottom number is the bass note), but a number followed by another number after a slash (and no bass implied) is read as a secondary function. Context decides which.

Rhythm and bar marks

NNS charts pack rhythm into the same line as the chords. A few common conventions:

Diamond ◊ over a number — hold the chord (whole note); the band stops driving the rhythm.
Marcato ^ over a number — short, pushed accent (think a stab on the downbeat).
Dot · over a number — staccato (clipped strum).
Underline beneath two or more numbers — the chords share a bar, splitting the beats evenly. 1 4 on its own = one bar each; 1 4 = two beats each in one bar.
Push < before a number — anticipate the chord by an eighth note (lands on the “and” of the previous beat).
Repeat bar %, often inside a slash — play the previous bar again.

Bar lines are usually implied by spacing: each blank-separated chord is its own bar unless underlined or grouped.

Reading a short chart

Here is a 12-bar progression in NNS:

Verse:    1   1   4   1
          5   4   1   5

Chorus:   6−  4   1   5
          6−  4   1 5  1

In the key of G major:

Verse:    G   G   C   G
          D   C   G   D

Chorus:   Em  C   G   D
          Em  C   G D  G

In the key of D major: D, D, G, D — A, G, D, A — Bm, G, D, A — Bm, G, D A, D. Same chart, two transpositions, no rewriting.

Why use it

Instant transposition — a singer can ask for the song down a step and you read the same paper.
Function over name — you see the harmony as 1–4–5 or 6−–4–1–5 instead of memorizing chord letters, which makes patterns across songs obvious.
Compact — a whole song fits on a single page; arrangements, repeats, and rhythm marks live next to the numbers.
Universal in country, gospel, rock, and pop — most Nashville session work uses NNS as the default chart format.

Minor keys

In a minor key, the conventional approach is to keep the numbers anchored to the major scale of the same letter: a song in A minor still calls the A chord 1 and the C chord b3. That way, modulating to the relative or parallel major changes only a few marks, and players who learn diatonic harmony in the major key can read minor charts without a separate system.

Some charts instead use an Aeolian frame where the tonic minor is 1− and the relative major is b3 — both styles exist; check the chart's first chord to know which convention the writer is using.

Explore further

Connect the numbers to the rest of the site:

Intervals — the building blocks the scale degrees come from.
Chord types & construction — how triads and seventh chords are built on each degree.
Circle of fifths — see how 1, 4, and 5 sit next to each other in any key.
Diatonic chord finder — show all seven diatonic chords for any key, ready to map onto NNS numbers.
Progression builder — sketch out 1–4–5, 1–5–6−–4, and other shapes by ear.
Guitar progressions — common NNS shapes shown on the fretboard.