The number of degrees of freedom, F, that a system containing C components can have when P phases are in equilibrium, is given as: \[F=C- P+2\]
Source:
PAC, 1994, 66, 577. 'Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)' on page 588 (https://doi.org/10.1351/pac199466030577)