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The Biot-Savart law can be stated in either of the following ways Differential form:    where DH is the contribution from a current I in an element Dl to the magnetic field strength at the point P which is at a displacement r relative to the location of Dl (see figure on right). or Integral form:     where H is the magnetic field strength at the point P in the figure.

IMPORTANT NOTE

Almost all presentations of the Biot-Savart law in textbooks and on the internet involve, once again, expressions for what they call 'magnetic field'; this corresponds to magnetic flux density in ÉîÒ¹ÑÇÖÞ¸£Àû¾Ã¾Ã Physics. As explained in Section 18.5, magnetic flux density (B) is directly proportional to the magnetic field strength (H). Note, however, that H depends only on the current and on the geometry of the circuit while B also depends on the medium in which the system is immersed. The aforementioned presentations invariably confine their discusion to magnetic fields arising from electric currents in vacuum.

As pointed out in the footnote on page 393 of Understanding Physics, the term 'magnetic field' is not recommended by the International Union of Pure and Applied Physics.