Help: Magnetic Field Component Grid Calculator

Known Issues

Certain Browsers: We have noticed that the calculator does not work on certain combinations of Windows OS and Internet Explorer. Should you notice this issue, please send us your versions of Windows and IE to geomag.models@noaa.gov along with a short description of the issue. An immediate workaround is to use Chrome or Firefox browsers.

Use the "Calculate Magnetic Field Component Grid" form under the "Magnetic Field Grid" tab of the Magnetic Field Calculators page, then click "Calculate" at the bottom. Below is an explanation of each of the sections contained within the calculator form.

Location

Max Longitude: The eastern most longitude value. Entered in either "decimal degrees" or "degrees minutes and seconds (space separated integers)"
Min Longitude: The western most longitude value. Entered in either "decimal degrees" or "degrees minutes and seconds (space separated integers)"
Lon Step Size: The interval that you would like your longitude range to be calculated with. For example, if you enter 100 W for your min longitude, and 180 W for your max longitude, and a step size of 10, you will get results for longitude values 100 W, 110 W, 120 W, 130 W 140 W, 150 W, 160 W, 170 W, and 180 W.
Max Latitude: The northern most latitude value. Entered in either "decimal degrees" or "degrees minutes and seconds (space separated integers)"
Min Latitude: The southern most latitude value. Entered in either "decimal degrees" or "degrees minutes and seconds (space separated integers)"
Lat Step Size: The interval that you would like your latitude range to be calculated with. For example, if you enter 20 N for your min latitude, and 90 N for your max latitude, and a step size of 10, your will get results for latitude values 20 N, 30 N, 40 N, 50 N 60 N, 70 N, 80 N, and 90 N.
Elevation: Elevation is especially important when computing the magnetic field at aircraft or higher altitudes. If you are unsure of your elevation, and are interested in a location on the surface of Earth, the default of 0 is sufficient.

GPS: The height above the World Geodetic System (WGS-84) ellipsoid.

MSL: Approximate height above mean sea level. More precisely it is height above the surface of the geoid defined by the Earth Gravitational Model 1996 (EGM96).
NOTE: The grid calculator allows for calculation of magnetic field values for an area or a point. In order to calculate a grid of components for an area, you fill out min and max longitude and min and max latitude values in order to define a bounding box for the area of interest. To get the components for a single point, the min and max longitude values should be the same, and the min and max latitude values should be the same. For example:

To input an area:

Max longitude = 85 1 39.6192 W
Min longitude = 125 1 39.6192 W
Lon Step Size = 1.0
Max latitude = 60 3 3.7836 N
Min latitude = 20 3 3.7836 N
Lat Step Size = 1.0

To input a point:

Max longitude = 105 1 39.6192 W
Min longitude = 105 1 39.6192 W
Lon Step Size = 1.0
Max latitude = 40 3 3.7836 N
Min latitude = 40 3 3.7836 N
Lat Step Size = 1.0

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°.

Component

Magnetic component: The component of the magnetic field you wish to calculate the grid for.

Model

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 scientific community's voluntary research under the banner of the International Association of Geomagnetism and Aeronomy (IAGA). The IGRF is retrospectively updated, and valid for the years 1900-2029. IGRF model details. For years from 1590 to 1900 the IGRF calculator was based on the gufm1 model. A smooth transition from gufm1 to IGRF was imposed from 1890 to 1900.

The World Magnetic Model (WMM) and the World Magnetic Model High Resolution are produced for the U.S. and U.K. defense agencies with guaranteed quality, user support, and updates. The WMM and WMMHR are predictive-only model and is valid for the current epoch, 2024-2029. WMM Model details.

The IGRF and WMM are both estimated from the most recent data and are of comparable quality. The WMMHR is an advanced geomagnetic field model that provides a more detailed, accurate depiction of the geomagnetic field than the World Magnetic Model (WMM). WMMHR model details.

Date Range

Start Date: The year you wish the magnetic field calculations to begin with. (Defaults to the current date). Note that for WMM and WMMHR models, the start date is 11/13/2024.

End Date: The year you wish the magnetic field calculations to end with. (Defaults to the current date).

Step size: The interval that you would like your date range to be calculated with. For example, if you select 2010 for your start date, and 2014 for your end date, and a step size of 2, you will get declination values for 2010, 2012, 2014 (every 2 years).

Result Format

The format you wish to view the results in. This allows you to view the results in a separate browser window (HTML), XML, or as comma separated values (CSV).

Using the programmatic interface

The calculator provides an easy way for you to get results in HTML, XML, CSV, or JSON programmatically (API). This information is available to you after a mandatory user registration. For registering, use the “API Registration” link in the top right corner.

Interpreting Results

Declination: The angle of difference between true North and magnetic North. For instance, if the declination at a certain point were 10° W, then a compass at that location pointing north (magnetic) would actually align 10° W of true North. True North would be 10° E relative to the magnetic North direction given by the compass. Declination varies with location and slowly changes in time.

Inclination: At a given location, the Inclination is the angle between the magnetic field vector and the horizontal plane (the plane is tangent to the surface of the Earth at that point). The inclination is positive when the magnetic field points downward into the earth and negative when it points upward.

Horizontal Intensity: The intensity of the component of the magnetic field is tangent to the Earth's surface at a given point.

North Component: The portion of the magnetic field that is directed horizontally northward. A southward directed field would have a negative value for the North component.

East Component: The portion of the magnetic field that is directed horizontally eastward. A westward directed magnetic field has a negative value for the East component.

Vertical Component: The portion of the magnetic field that is directed perpendicular to the Earth's surface at a given location. Down is measured as positive and up as negative.

Total Field: The intensity (or strength) of the entire magnetic field at a given location. Geometrically, it is the length of the magnetic field vector.

Change/year: The total amount each component has changed between the calculated year, and the year before it.

Uncertainty: The one standard deviation difference between a hypothetical measurement and the calculator result. For more information see our page on the >WMM limitations.

Blackout Zone: The calculator outputs a warning if the location is in the blackout zone around the magnetic pole as defined by the WMM military specification. Compass accuracy is highly degraded in this region. [triggered if H < 2000 nT].

The calculator outputs a caution if location is approaching the blackout zone around the magnetic pole as defined by the WMM military specification. Compass accuracy may be degraded in this region.” [triggered if 2000 nT <= H < 6000 nT]

For more information, visit the FAQ page

https://www.ncei.noaa.gov/products/geomagnetism-frequently-asked-questions.
*Accuracies for the angular components (Declination, D and Inclination, I) are reported in degrees and minutes of arc and are generally within 30 minutes.

*Accuracies for the force components (Horizontal - H, North - X, East - Y, Vertical - Z, and Total force - F) are generally within 100 to 250 nanotesla.

Height Validity: In general, the WMM model is expected to meet the WMM military specification from the ground (or from 1 km under the sea level) up to 1900 Km. However, the height validity of WMM is dependent on the geomagnetic activity level. More detailed information is available here.

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