Magnetic Declination Formula

Magnetic declination is defined as the angle between magnetic north and true north on the horizontal plane, which is not constant and keeps changing depending upon the position on the earth’s surface and time. The Greek letter δ is used as the symbol for magnetic declination and is also known as magnetic variation.

Magnetic Declination is also referred to as the magnetic variation. Magnetic Declination is represented in the Greek word.

\(\begin{array}{l}\delta = Magnetic\,Declination\end{array} \)

Magnetic Declination is associated with the year, longitude and latitude of a given location.

Calculation Of Magnetic Declination

Following are the different ways used to calculate the magnetic declination:

  • Using the declination calculator: The information such as year, latitude and longitude of the given location should be provided and the calculator gives the declination on the basis of magnetic reference field models.
  • Using a magnetic declination chart: A magnetic declination chart is a map with the earth’s magnetic fields available on it.
  • Using a compass: There are three types of bearing, they are true, magnetic and compass bearing. A compass can be used to calculate the declination as it is one of the errors of the compass and the other is magnetic variation. These three are related by:

T = M + V

M = C + D

T = C + V + D (which is a general equation relating compass and true bearings)


C = Compass Bearing

M = Magnetic Bearing

T = True Bearing

V = Variation

D = Compass Deviation

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