Magnetic Declination Calculator (MagDec)

This page describes a free application that runs in the Google Earth desktop client. Please install Google Earth, download MagDec, and return to this page to learn more.

MagDec is a graphical front end for the NGDC online Magnetic Field Calculators. It eliminates the need to input geodetic coordinates and displays the calculated magnetic declination and secular variation in a placemark balloon.

  1. Position the point of interest (POI) in the center of the view. One way to do this is to double-click an unmarked location. To precisely position the POI in the center of the view, add a placemark at the desired location; then edit the properties of that placemark and reset the view (explain). For best results, disable automatic tilting (Tools, Options, Navigation, Do not automatically tilt while zooming) and minimize elevation exaggeration (Tools, Options, 3D View, Elevation Exaggeration, 0.01).
  2. Check the box beside the Declination Calculator network link. A form will be presented with read-only coordinates corresponding to the view center and input fields for year, month, and day. Calculated magnetic declination and secular variation are displayed when the Calculate button is pressed.
  3. On subsequent uses, reposition the POI and ensure that the network link is checked and selected. Then choose Refresh from the Edit menu, or right-click and select Refresh in the context menu (explain).

Image NGDC

MagDec provides global coverage for 1900 to 2019 using the International Geomagnetic Reference Field (IGRF) (1900-2014) and the World Magnetic Model (WMM) (2015-2019). Coverage of the conterminous United States for 1750 to 1899 is provided by the Historical Declination Calculator. Historical declination values are not available for all years in all areas.

Note: To save MagDec results from one Google Earth session to another, right-click on Saved Placemarks and select Save to My Places.

All data are retrieved from remote servers. Data errors, accuracy, and availability are beyond the control of this application.