What rule gives the direction of the magnetic field around a straight current-carrying wire?

The right-hand grip rule gives the direction of the magnetic field around a straight current-carrying wire.

Point the right thumb in the direction of conventional current. The curled fingers then show the direction of the circular magnetic field lines around the wire. Reversing the current reverses the field direction, while increasing the current strengthens the field.

The field around a long straight wire forms concentric circles. Its magnitude decreases with distance from the wire and depends on the current and the magnetic permeability of the surrounding material. This relationship is a direct consequence of Ampère’s circuital law for the idealized straight-wire case.

The rule uses conventional current, defined as the motion of positive charge. In a metal, electrons usually drift in the opposite direction, so using electron motion directly without reversing the direction can produce an incorrect field orientation.