The rule used to determine the direction of magnetic field around a current carrying straight conductor is :

The direction of the magnetic field produced around a straight current-carrying conductor is given by the Right-hand thumb rule (also called Maxwell's corkscrew rule). It states: if the thumb of the right hand points in the direction of current flow, the curl of the fingers gives the direction of the magnetic field lines. Fleming's left-hand rule gives the direction of force on a current-carrying conductor in a magnetic field; Fleming's right-hand rule applies to induced current direction in a generator; Hund's rule is a chemistry/atomic-physics rule about electron filling.