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Compute Earth's Magnetic Field Values

On-line calculators to estimate current and past values of the magnetic field.

If you want only the magnetic declination (variation) for a single day between 1900-present, visit our declination calculator.

If you want all seven magnetic field components for a single day or range of years from 1900-present, please visit our Magnetic Field Calculator . Please read the instructions below before using this calculator.

U.S. Historic Declination calculator This calculator uses the US declination models to compute declination only for the conterminous US from 1750 - present. Due to differences in data availability (recorded observations of the magnetic field), the western part of the US may not have values until the early 1800's.

You can also compute values for an area. See the instructions for area.

Solar disturbances can cause significant differences between the estimated and actual field values. You can check the current solar conditions from NOAA's Space Environment Center.

Values are computed using the current International Geomagnetic Reference Field as adopted by the International Association of Geomagnetism and Aeronomy. Values are estimates based on the IGRF10 and are generally accurate to within 30 minutes of arc for D and I and 100-250 nT for the force elements (F, H, Z, X, and Y).

Input required is:

  1. Location (latitude and longitude), entered either in decimal degrees or degrees minutes and seconds (space separated integers).
    note: If you do not know your latitude and longitude and you live in the United States, enter your zip code in the box provided and use the "Get Location" button or the country - city select boxes on the left. Links are also provided to the U.S. Gazetteer and the Getty Thesaurus, good sources of latitude / longitude information for the U.S. and World respectively.
  2. Elevation (recommended for aircraft and satellite use) in feet, meters, or kilometers above mean sea level.
  3. Date in Year, Month, Day (form defaults to the current day). There are two date entries providing the ability to compute the magnetic field values over a range of years. Both dates default to the current day. If you want only the current field values, you do not need to enter anything else! If you want to know the magnetic field values for a range of years (i.e. from 1960 - 2004), enter the oldest date in the Start Date box and the most recent date in the End Date box.
  4. Date Step Size (used only for a range of years) is the number of years between calculations. For example, if you want to know the magnetic field values from 1960 through 2004 for every two years, enter 1960 for the Start Year, 2004 for the End Year, and 2 for the Step Size.
  5. To compute your field values, hit the Compute! button.

Results include the seven field parameters and the current rates of change for the final year:

  • Declination (D) positive east, in degrees and minutes
    Annual change (dD) positive east, in minutes per year
  • Inclination (I) positive down, in degrees and minutes
    Annual change (dI) positive down, in minutes per year
  • Horizontal Intensity (H), in nanoTesla
    Annual change (dH) in nanoTesla per year
  • North Component of H (X), positive north, in nanoTesla
    Annual change (dX) in nanoTesla per year
  • East Component of H (Y), positive east, in nanoTesla
    Annual change (dY) in nanoTesla per year
  • Vertical Intensity (Z), positive down, in nanoTesla
    Annual change (dZ) in nanoTesla per year
  • Total Field (F), in nanoTesla
    Annual change (dF) in nanoTesla per year

You can see more information on the required input or results. For more information on magnetism, adjusting your compass, computing bearings, please see our Answers to Frequently Asked Questions (FAQ) page. Go to Compute the Field Values

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Required Input

Entering location information

If you are interested in a location within the USA, you can enter your postal zip code in the space provided and press the "Get Location" button. The latitude and longitude for that postal zip code (as stored in the U.S. Census Bureau), will automatically be populated in the location area. If no value appears, it is likely there was a problem obtaining a location for the zip code entered. In this case, please enter the latitude and longitude directly in the boxes provided.

If you are entering the location in degrees, minutes, and seconds, please enter values for all three - separated by spaces - even if the value is zero. For example, if your location is at latitude 35° 30' 0", enter 35 30 0. 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! Instead, please be sure the proper selection to the right of the box is checked for your location. N stands for northern hemisphere latitude, S for southern hemisphere latitude, W for western hemisphere longitude, E for eastern hemisphere longitude. The USA is (mostly) located in the northern (N) and western (W) hemisphere.

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 degrees and westward across the Atlantic to 90° West (Jackson, MI) to 180 degrees west. For example, the location of Louisville, KY USA is 38.2247° N, 85.7412° W also expressed as 38° 13' 29" N, 85° 44' 28" W.

Entering date information

There are two date entries providing the ability to compute the magnetic field values over a range of years. If you want a range of dates, enter your oldest date in the "Start Date " field, your most recent date in the "End Date" field, and enter the number of years between computations in the "Date Step Size" field. For example, if you want to know the magnetic field values from 1900 through 2010 at 5 year intervals, enter 1900 1 1 for the start date, 2010 1 1 for the end date, and 5 for the step size. The end date must be greater than or equal to the start date. Do not enter a step size (default is zero) if you are not computing a range of years.

The IGRF magnetic field model is updated every 5 years to enable forward computing of the magnetic field. For example, the IGRF10 adopted in 2005 was valid through January 1 2010. If you enter an end date beyond the valid period of the model, you will get an error message requesting you to enter a valid date.

Entering 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. Please enter the elevation in either Kilometers (-1 to 600)

Click on the "Compute" button when ready.

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Area Input

To compute the field values for an area, please enter the northern most and southern most latitude, the step size for latitude, the western most and eastern most longitudes and the step size for longitude. For example, if you are interested in declination grid for the conterminous U.S. with values computed every 5 degrees of latitude and longitude, you would enter (click on example for larger image):

snap shot of area entry

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Reading the results

The magnetic parameters declination, inclination, horizontal component, north component, east component, vertical component, and total field (D, I, H, X, Y, Z, and F) are computed based on the latest International Geomagnetic Reference Field (IGRF) model of the Earth's main magnetic field. 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. Local disturbances and attempting to use a model beyond its valid date range could cause greater errors. Before using the IGRF please look at the 'Health Warning'. The sign convention used throughout is Declination (D) positive east, Inclination (I) and Vertical intensity (Z) positive down, North component (X) positive north, and East component (Y) positive east. The Horizontal (H) and Total (F) intensities are always positive. For more information on Earth's magnetic field parameters, see our Frequently Asked Questions.


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