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The basic equation governing the magnetic field due to a current distribution is the Biot-Savart Law. Finding the magnetic field resulting from a current distribution involves a vector product and becomes an inherent calculus problem when the distance from a current to the field point is continuously changing.

According to this law, the magnetic field at a point due to a current element of length dl carrying a current I, at a distance r from the element is

dB = (μ_o/4π) I (dl x r)/r³.

Biot-Savart Law has certain similarities as well as difference with Coulomb's Law for electrostatic field as there is an angle dependence in Biot-Savart Law which is not present in electrostatics.

Biot-Savart law can be expressed alternatively as : 

Ampere's Circuital law

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