Each major has a relative minor so that means that however many sharps/flats are in that major key, that’s also how many sharps/flats are in the relative minor key. For example:
G major/E minor – 1 Sharp
D major/ B minor – 2 Sharps
A major/ F# minor – 3 Sharps
E major/ C# minor – 4 Sharps
B major/ G# minor – 5 Sharps
F# major/ D# minor – 6 Sharps
Then going anti-clockwise:
F major/ D minor – 1 Flat
Bb major/ G minor – 2 Flats
Eb major/ C minor – 3 Flats
Ab major/ F minor – 4 Flats
Db major/ A# minor – 5 Flats
Gb major/ D# minor – 6 Flats