Mixing in key: which keys go together, and can you trust a key reading?

Published 2026-10-09 · by patrick-eu

Short answer: two songs mix in key when their keys share most of their notes. On the key wheel DJs use (numbers 1 to 12, A for minor, B for major), that means the same number, or one number up or down. We counted the notes for all 576 pairs of keys:

Same code, or same number with the other letter (8A and 8B, A minor and C major): 7 of 7 notes shared.
One number up or down, either letter (8A to 7A, 9A, 7B or 9B): 6 of 7.
Two numbers away: 5 of 7. Five or six away: only 2 of 7. A song pitched up one semitone moves five numbers round the wheel, so it lands on one of the worst matches.

To read each song's key, drop it into the BPM and key finder. In our test it read the exact key on 78 of 96 test songs, and every one of the 18 misses was the relative key: the same number with the other letter, which shares all 7 notes. So a wrong reading still pointed to a safe mix. Then order the songs with the table below and join them in the audio joiner.

Why neighbouring keys mix

A major or minor key uses 7 of the 12 notes. Two songs in keys that use the same notes can play over each other without a clash; the more notes they differ on, the more their melodies and chords rub.

The wheel puts keys in order of the circle of fifths: each step adds or removes one sharp or flat, so it changes exactly one note. The A and B rings hold a minor key and the major key that uses the same 7 notes (its relative major). That is why counting steps on the wheel works as a quick rule.

The numbers and letters below follow the "Lancelot" key notation in the open-source DJ program Mixxx, as defined in its source file src/track/keyutils.cpp (read 2026-10-09): a number from 1 to 12, then A for a minor key or B for a major key. Its list of compatible keys for any key is the key itself, the other letter on the same number, and one number up or down on both letters. If your DJ program shows a different code, go by the key name.

Key names are spelled as the key finder on this site shows them (it writes D♭ major but C♯ minor, A♭ major but G♯ minor). Mapping from Mixxx keyutils.cpp, read 2026-10-09; checked by our script against four known points (8B C major, 8A A minor, 1B B major, 1A G♯ minor).
Number	A (minor)	B (major)
1	G♯ minor	B major
2	E♭ minor	F♯ major
3	B♭ minor	D♭ major
4	F minor	A♭ major
5	C minor	E♭ major
6	G minor	B♭ major
7	D minor	F major
8	A minor	C major
9	E minor	G major
10	B minor	D major
11	F♯ minor	A major
12	C♯ minor	E major

How many notes each move keeps

We wrote out the 7 notes of every key (major scale and natural minor scale) and counted the notes shared by each of the 576 ordered pairs, then grouped the pairs by how far apart they sit on the wheel. Every pair in a group gave the same count:

Counted by script, 2026-10-09: 24 keys × 24 keys, major and natural minor scales. A minor song with a raised seventh (as in many classical pieces) adds one note outside this count.
Move on the wheel	Example from 8A (A minor)	Notes shared
Same code	8A A minor	7 of 7
Same number, other letter	8B C major	7 of 7
One number up or down, same letter	7A D minor, 9A E minor	6 of 7
One number up or down, other letter	7B F major, 9B G major	6 of 7
Two numbers away, either letter	10A B minor, 6B B♭ major	5 of 7
Three numbers away	11A F♯ minor, 5B E♭ major	4 of 7
Four numbers away	12A C♯ minor, 4B A♭ major	3 of 7
Five or six numbers away	3A B♭ minor, 2B F♯ major	2 of 7

The same count shows what changing the pitch does. Raising a whole song by one semitone moves it five numbers back on the wheel (8A to 3A), down to 2 shared notes with where it started. Raising it by two semitones moves it two numbers forward (8A to 10A), 5 shared notes. Raising it by seven semitones is one number forward. So a "small" pitch change of one semitone is the biggest jump in key, and the two neighbours on the wheel are a fifth apart, not a semitone apart. This site has no pitch or tempo change, so the order of the songs is the tool you have.

How we tested the key finder

Tool: this site's BPM and key finder, the real page run on a local copy in Chromium 153 through Playwright 1.63 (headless). Our script picked each file in the page's file box and read the key, the "Next closest" line and the confidence line.
96 test songs we made, so the true key is known: four chord patterns in all 12 keys, each as a 30 s and a 10 s file (44.1 kHz, 16-bit mono WAV, 110 BPM, plucked chords on every beat, a bass note per bar, kick and hi-hat). Major I–IV–V–I and I–V–vi–IV; minor i–iv–V–i (with the raised seventh) and i–VI–III–VII (natural minor, the pattern of many pop songs in minor).
One real recording: Mozart's Symphony No. 40 in G minor, first movement, played by the Musopen Symphony, in the public domain on Wikimedia Commons, converted to 44.1 kHz, 16-bit: the whole movement (5:58.8) and its first 30 s. The true key is the one in the title. The finder gives one key for a whole file.

What the key finder read

Measured by snipaudio.com, 2026-10-09, headless Chromium 153. Each 30 s file took at most 0.85 s from picking it to the result; the 6-minute Mozart file took 6.7 s.
Test songs	Files	Exact key	Relative key instead	Confidence said Weak
Major I–IV–V–I, 30 s and 10 s	24	24	0	0
Major I–V–vi–IV, 30 s and 10 s	24	24	0	0
Minor i–iv–V–i, 30 s and 10 s	24	24	0	0
Minor i–VI–III–VII, 30 s	12	2	10	5
Minor i–VI–III–VII, 10 s	12	4	8	5
Mozart No. 40 (G minor), whole movement and first 30 s	2	2	0	0

Every miss was the same kind: a minor song read as its relative major, for example C minor read as E♭ major (5A read as 5B). That is the only mix-up we saw, on the one pattern where the minor chord is just one of four chords that all belong to the major key too. When the song leaned on its home chord with the raised seventh (i–iv–V–i), the finder never missed.

The confidence line did not flag most misses: 12 of the 18 wrong readings said Clear. What did flag them is the line under the result. On all 24 songs of that pattern, the first key in "Next closest" was the relative key, marked "(relative minor)" or "(relative major)".

For mixing, that miss costs nothing: 5A and 5B share all 7 notes, so both readings lead to the same neighbours on the wheel. It only matters if you care about the mood label, minor or major.

How to put a set in key with this site

Read each song's key in the BPM and key finder and look it up in the table above. Note the tempo too: the finder shows it next to the key.
If the reading is minor or major and the first "Next closest" key is marked relative, treat both as the same number on the wheel. You do not need to decide which is right to mix.
Do not use the rest of the "Next closest" list as safe keys. On our minor i–iv–V–i songs the first alternative was the major key on the same note (C minor, then C major). That is three numbers away on the wheel (5A to 8B): 4 of 7 notes.
Order the songs so each step is the same number or one number up or down. Going round the wheel one step at a time (8A, 9A, 10A, ...) changes one note per song.
Join them in the audio joiner with a crossfade; how long a crossfade should be has measured lengths. The joiner does not change tempo or pitch, so songs with very different tempos will not line up beat to beat during the overlap.

Questions

Is the relative minor the same as the key one step away?

No. The relative minor or major is the same number with the other letter (8B C major and 8A A minor) and uses exactly the same 7 notes. One step away (8B to 9B, C major to G major) changes one note.

Can a key finder tell a minor song from its relative major?

Not always, because the notes are the same; only which chord feels like home differs. In our test the finder on this site mixed them up on 18 of 24 songs built on i–VI–III–VII, and on none of the other 74 files.

Does the key finder show the wheel codes?

No, it shows the key name, for example A minor or F♯ major. Use the table above to turn it into a number and letter.