Magnetic Declination Calculator Usa
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Reviewed by Calculator Editorial Team
Magnetic declination is the angle between true north and magnetic north at a specific location. This calculator helps you determine the magnetic declination for any point in the USA, which is essential for accurate compass navigation and surveying.
What is Magnetic Declination?
Magnetic declination is the angle between true north (geographic north) and magnetic north (the direction a compass points). This variation changes over time and differs by location due to the Earth's magnetic field.
In the USA, magnetic declination can range from -20° to +20° depending on the location. A positive value means magnetic north is east of true north, while a negative value means it's west of true north.
Magnetic declination is not the same as magnetic inclination (the angle between the magnetic field and the horizontal plane).
How to Use This Calculator
- Enter the latitude and longitude of your location in decimal degrees.
- Select the year for which you need the magnetic declination.
- Click "Calculate" to get the result.
- Review the result and chart showing the declination over time.
The calculator uses the World Magnetic Model (WMM) to provide accurate results. The WMM is updated every 5 years by the National Oceanic and Atmospheric Administration (NOAA).
How Magnetic Declination is Calculated
The magnetic declination is calculated using the World Magnetic Model (WMM), which is a standard model of the Earth's large-scale magnetic field. The WMM provides the magnetic declination for any location and time.
Formula: Magnetic Declination = arctan2(Y, X)
Where:
- X = Magnetic field strength in the north direction
- Y = Magnetic field strength in the east direction
The WMM is updated every 5 years by NOAA to maintain accuracy. The most recent model is valid from 2020 to 2025.
Example Calculation
Let's calculate the magnetic declination for New York City (40.7128° N, 74.0060° W) in 2023.
- Enter latitude: 40.7128
- Enter longitude: -74.0060
- Select year: 2023
- Click "Calculate"
The calculator will display the magnetic declination for New York City in 2023, which is approximately 13.5° west.
| Location | Latitude | Longitude | Year | Declination |
|---|---|---|---|---|
| New York City | 40.7128° N | 74.0060° W | 2023 | 13.5° W |
| Los Angeles | 34.0522° N | 118.2437° W | 2023 | 15.2° W |
| Chicago | 41.8781° N | 87.6298° W | 2023 | 1.2° W |
FAQ
What is the difference between magnetic declination and magnetic inclination?
Magnetic declination is the angle between true north and magnetic north, while magnetic inclination is the angle between the magnetic field and the horizontal plane. Declination affects compass navigation, while inclination affects the angle of a magnetic compass needle.
How often is the World Magnetic Model updated?
The World Magnetic Model is updated every 5 years by the National Oceanic and Atmospheric Administration (NOAA). The most recent update was in 2020, making the model valid from 2020 to 2025.
Why does magnetic declination change over time?
Magnetic declination changes over time due to the movement of the Earth's magnetic field. This movement is influenced by the Earth's core dynamics and can cause the magnetic poles to shift.