Magnetic components

The Earth's magnetic field is a vector quantity; at each point in space it has a strength and a direction. To completely describe it we need three quantities. These may be:

  • three orthogonal strength components (X, Y, and Z);
  • the total field strength and two angles (F, D, I); or
  • two strength components and an angle (H, Z, D)

The relationship between these 7 elements is shown in the diagram.

Magnetic elements
Magnetic components
Component Description
F the total intensity of the magnetic field vector
H the horizontal intensity of the magnetic field vector
Z the vertical component of the magnetic field vector; by convention Z is positive downward
X the north component of the magnetic field; X is positive northward
Y the east component of the magnetic field; Y is positive eastward
D magnetic declination, defined as the angle between true north (geographic north) and the magnetic north (the horizontal component of the field). D is positive eastward of true North.
I magnetic inclination, defined as the angle measured from the horizontal plane to the magnetic field vector; downward is positive

D and I are measured in degrees. All other elements are measured in nanotesla (nT; 1 nT = 10-9 Tesla).

The seven elements are related through the following simple expressions.

Declination (D) D = tan -1 ( Y X ) Inclination (I) I = tan -1 ( Z H ) Horizontal (H) H = X 2 + Y 2 North (X) X = H cos ( D ) East (Y) Y = H sin ( D ) Intensity (F) F = X 2 + Y 2 + Z 2

Use the magnetic field calculator to calculate the magnetic elements for any location.