Using the "Calculate Declination" form under the "Declination" tab of the Magnetic Field Calculators page, click "Calculate" at the
bottom. Below is an explanation of the each of the sections contained within the calculator form.
Latitude and Longitude: Entered in either
"decimal degrees" or "degrees minutes and
seconds (space separated integers)"
If you do not know the longitude and latitude, use Lookup Latitude / Longitude in the box to the right of the calculator,
which will populate the longitude and latitude values in the calculator form for you.
If Lookup Latitude / Longitude can't find your location, search for an address at USGS Earth Explorer.
Enter the latitude and longitude into the calculator form on the left.
If the location is in degrees, minutes, and seconds, please enter the values
separated by a single space. Remember, there are 60 seconds in a minute and 60 minutes in a
degree, therefore 35° 30' 0" is equivalent to 35.500. Do not enter the N, S, E, or W
designation in the box! The box should be a positive value and the hemisphere should be designated
by selecting a value from the choices to the right of the text field. N stands for northern
hemisphere latitude, S for southern hemisphere latitude, W for western hemisphere longitude, and E
for eastern hemisphere longitude. The USA is (mostly) located in the northern (N) and western (W)
hemispheres, which have been pre-populated for you. Latitude ranges from 90° south
(south pole) to 90° north (north pole) with 0° meaning the equator. Longitude ranges from
0° (Greenwich, England) eastward through 90° East (Bangladesh) to 180° and westward
across the Atlantic from 90° West (Jackson, MI) to 180°.
Model: The model you wish to use for calculating the magnetic field.
The magnetic field calculator supports two models. The International Geomagnetic Reference Field (IGRF) is produced by the voluntary research of the scientific community under
the banner of the International Association of Geomagnetism and Aeronomy (IAGA).
The IGRF is retrospectively
updated, and valid for the years 1590-2019. IGRF model: http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html.
The World Magnetic Model (WMM) is produced for the U.S. and U.K. defense agencies with guaranteed
quality, user support, and updates. The WMM is a predictive-only model and is valid for the current
epoch, 2014-2019. WMM model details: http://ngdc.noaa.gov/geomag/WMM.
The IGRF and WMM are both estimated from the most recent data and are of comparable quality.