How does Circle of Fifths key matching work?

Keys that are adjacent on the Circle of Fifths (a perfect fifth apart) or that share a relative major/minor sound harmonically smooth together. This is the basis of the Camelot wheel DJs use for harmonic mixing.

What BPM difference is too large to blend?

As a rule of thumb, within about 6 percent of each other beatmatches cleanly. Beyond that you'll hear pitch or timing drift unless you use half-time/double-time, which the checker also tests for.

Why specify key and BPM in an AI music prompt?

Tools like Suno and Udio respond to explicit "120 bpm" and key tags, helping match a generation to an existing track. It keeps multiple generations in the same project harmonically and rhythmically consistent.

Does relative major/minor count as compatible?

Yes. A major key and its relative minor (e.g. C major and A minor) share the same notes and are considered a perfect harmonic match — the checker flags these explicitly.

BPM & Key Compatibility Checker

BPM and key compatibility checker

Whether you’re layering two AI generations, building a mashup, or planning a DJ transition, two tracks blend cleanly only when their keys are harmonically related and their tempos are close enough to beatmatch. This tool checks both at once: it places your two keys on the Circle of Fifths to rate harmonic compatibility, and compares the BPMs (including half- and double-time) to judge the tempo match.

How it works

Each key maps to a position on the Circle of Fifths, the same structure behind the DJ “Camelot wheel.” Two keys are rated by their distance on the circle: identical keys are perfect, relative major/minor pairs are perfect, neighbours one step apart are compatible, and keys far apart clash. For tempo, the tool computes the percentage difference and also checks whether one BPM is roughly half or double the other — a common, musically valid relationship that lets very different-feeling tempos lock together.

Tips for harmonic mixing

Stay within one step on the circle. Moving to an adjacent key (a perfect fifth) is the smoothest transition; jumping across the circle sounds jarring.
Relative major/minor is a free swap. C major and A minor share all their notes — use this to add contrast without clashing.
Use half/double time for tempo gaps. A 70 BPM ballad and a 140 BPM track share the same grid; the checker recognizes this.
State key and BPM in AI prompts. Adding “A minor, 120 bpm” keeps multiple generations consistent so you can stitch them together later.