Key Signature Calculator

Key signatures are governed by the circle of fifths and a strict order of accidentals. Sharps follow the sequence F, C, G, D, A, E, B (mnemonic: Fat Cats Go Down Alleys Eating Birds), while flats follow the exact reverse: B, E, A, D, G, C, F (mnemonic: Beaver Eats All Day Get Coffee Fast). To find a major key with sharps, look at the last sharp in the key signature and go up one half-step. For flat keys, the second-to-last flat dictates the name of the major key. Minor keys are always found three half-steps down from their relative major scale.

Imagine you are analyzing a piece of sheet music and notice 3 sharps in the key signature (F#, C#, and G#). Using our calculator, you input '3' for the number of accidentals, select 'Sharps' as the accidental type, and choose 'Major' for the key quality. Following the rule, the last sharp is G#. Going up a half-step from G# brings us to A. Therefore, the key is A Major. For the relative minor, we go down three half-steps from A, revealing F# Minor as the matching minor key.

Memorize the order of sharps and flats to quickly verify calculator results by hand. Always double-check whether a piece is in a major or minor key by looking at the tonal center or final cadence chord, as relative keys share the exact same key signature. When transposing, remember that changing the key signature alters every corresponding note across all octaves unless an accidental explicitly modifies it.