Magnetic Declination Calculator

Calculate the angle between true north and magnetic north for any location on Earth.

Determine the magnetic declination at any location using latitude, longitude, and date. Essential for accurate navigation, surveying, and compass calibration.

Examples

Click on any example to load it into the calculator.

New York City, USA

North America

Typical magnetic declination for the northeastern United States.

Latitude: 40.7128 °

Longitude: -74.0060 °

Date: 2024-01-01

Altitude: 10 m

London, UK

Europe

Magnetic declination for Western Europe showing westward declination.

Latitude: 51.5074 °

Longitude: -0.1278 °

Date: 2024-01-01

Altitude: 35 m

Tokyo, Japan

Asia

Eastern declination typical for East Asia and the Pacific region.

Latitude: 35.6762 °

Longitude: 139.6503 °

Date: 2024-01-01

Altitude: 40 m

Sydney, Australia

Southern Hemisphere

Southern Hemisphere declination showing different magnetic field characteristics.

Latitude: -33.8688 °

Longitude: 151.2093 °

Date: 2024-01-01

Altitude: 19 m

Other Titles
Understanding Magnetic Declination: A Comprehensive Guide
Explore the fascinating world of Earth's magnetic field and learn how to navigate accurately using magnetic declination calculations. This guide covers everything from basic concepts to advanced applications in navigation and surveying.

What is Magnetic Declination?

  • Core Concepts
  • True North vs Magnetic North
  • Why It Matters
Magnetic declination is the angle between true north (geographic north) and magnetic north (the direction a compass needle points). This angle varies depending on your location on Earth and changes over time due to the dynamic nature of Earth's magnetic field. Understanding magnetic declination is crucial for accurate navigation, surveying, and any activity that relies on compass bearings.
The Earth's Magnetic Field
Earth's magnetic field is generated by the movement of molten iron in the outer core. This creates a complex field that extends from the Earth's interior into space. The magnetic poles are not aligned with the geographic poles, and they move over time. Currently, the magnetic north pole is located in the Arctic Ocean and is moving toward Siberia at about 55 kilometers per year.
True North vs Magnetic North
True north is the direction toward the geographic North Pole, which is the point where Earth's axis of rotation intersects the surface. Magnetic north is the direction a compass needle points, which is toward the magnetic north pole. The difference between these two directions is the magnetic declination. In some areas, this difference can be as much as 20 degrees or more.
Historical Context and Changes
Magnetic declination has been documented for centuries. Early navigators noticed that compass needles didn't always point true north, and this observation led to the development of magnetic declination charts. The field changes continuously, with some areas experiencing rapid changes while others remain relatively stable. These changes are tracked by magnetic observatories worldwide and incorporated into models like the International Geomagnetic Reference Field (IGRF).

Key Magnetic Declination Concepts:

  • East Declination: When magnetic north is east of true north (positive values)
  • West Declination: When magnetic north is west of true north (negative values)
  • Zero Declination: When magnetic north and true north align (agonic line)
  • Annual Change: The rate at which declination changes each year (typically 0.1-0.5° per year)

Step-by-Step Guide to Using the Calculator

  • Finding Your Coordinates
  • Entering Data
  • Interpreting Results
Using the magnetic declination calculator is straightforward, but accuracy depends on precise input data. Follow these steps to get the most reliable results for your location.
1. Determine Your Exact Coordinates
Use GPS, online mapping services, or topographic maps to find your precise latitude and longitude. Even small errors in coordinates can lead to significant differences in declination values, especially in areas with steep magnetic field gradients. For best results, use coordinates accurate to at least 0.01 degrees.
2. Choose the Appropriate Date
Magnetic declination changes over time, so it's important to use the date for which you need the calculation. For current navigation, use today's date. For historical analysis or future planning, use the relevant date. The calculator accounts for the secular variation of the magnetic field.
3. Consider Altitude Effects
While altitude has a relatively small effect on magnetic declination, it can be significant in mountainous regions or for aviation applications. Enter your altitude above sea level in meters. For most ground-based applications, you can leave this field empty or use 0.
4. Interpret the Results
The calculator provides four key values: Magnetic Declination (the main result), Magnetic Inclination (the angle the field makes with the horizontal), Total Field Intensity (the strength of the magnetic field), and Annual Change (how fast the declination is changing). Use the declination value to adjust your compass readings or navigation calculations.

Common Coordinate Sources:

  • GPS Devices: Most accurate for real-time navigation
  • Google Maps: Right-click on location to get coordinates
  • Topographic Maps: Use the grid system and interpolation
  • Smartphone Apps: Many navigation apps show coordinates

Real-World Applications and Navigation

  • Compass Navigation
  • Surveying and Mapping
  • Aviation and Maritime
Magnetic declination calculations are essential for numerous practical applications, from simple hiking navigation to complex surveying operations and aviation navigation.
Compass Navigation and Orienteering
For hikers, campers, and outdoor enthusiasts, understanding magnetic declination is crucial for accurate navigation. When using a map and compass, you must account for the difference between true north (shown on maps) and magnetic north (shown by your compass). Add the declination to your compass bearing when converting from map to compass, or subtract it when converting from compass to map.
Surveying and Land Measurement
Professional surveyors must account for magnetic declination when establishing property boundaries, creating maps, or conducting construction surveys. Even small errors in declination can compound over long distances, leading to significant positioning errors. Modern surveying equipment often includes built-in declination corrections.
Aviation and Maritime Navigation
Pilots and mariners rely on magnetic declination for navigation planning and instrument calibration. Aircraft compasses must be calibrated for the local magnetic environment, and flight planning software automatically accounts for declination changes along flight paths. Maritime charts include magnetic variation information for safe navigation.

Navigation Correction Examples:

  • If declination is 15° East: Add 15° to compass bearing to get true bearing
  • If declination is 10° West: Subtract 10° from compass bearing to get true bearing
  • For map reading: Use true north bearings from the map
  • For compass use: Apply declination correction to get true directions

Advanced Concepts and Magnetic Field Models

  • IGRF Model
  • Secular Variation
  • Magnetic Anomalies
The calculation of magnetic declination involves sophisticated mathematical models that account for the complex structure of Earth's magnetic field and its temporal variations.
International Geomagnetic Reference Field (IGRF)
The IGRF is a mathematical model of Earth's magnetic field that represents the field as a series of spherical harmonic coefficients. This model is updated every five years and provides the foundation for magnetic declination calculations worldwide. The model accounts for the main field generated in Earth's core, excluding local anomalies and external field variations.
Secular Variation and Field Changes
The Earth's magnetic field changes continuously over time scales ranging from years to centuries. These changes, known as secular variation, are caused by processes in Earth's outer core. The rate of change varies by location, with some areas experiencing rapid changes while others remain relatively stable. The calculator includes these temporal variations in its calculations.
Local Magnetic Anomalies
Local variations in Earth's crust can cause magnetic anomalies that affect declination values. These anomalies are caused by variations in the magnetic properties of rocks and are particularly significant in areas with high concentrations of magnetic minerals. While the calculator provides general declination values, local surveys may be necessary for high-precision applications in areas with known anomalies.

Magnetic Field Characteristics:

  • Field Strength: Ranges from about 25,000 to 65,000 nanotesla at Earth's surface
  • Inclination: Varies from 0° at the magnetic equator to 90° at the magnetic poles
  • Declination: Can range from -180° to +180°, with most values between -30° and +30°
  • Annual Change: Typically 0.1-0.5° per year, but can be higher in some regions

Common Misconceptions and Best Practices

  • Accuracy Limitations
  • When to Update
  • Alternative Methods
Understanding the limitations and proper use of magnetic declination calculations is essential for reliable navigation and surveying applications.
Accuracy and Precision Considerations
While magnetic declination calculators provide good estimates, they have limitations. The IGRF model has an accuracy of about 0.5° for most locations, but local anomalies can cause larger errors. For high-precision applications, local magnetic surveys may be necessary. Additionally, the model doesn't account for temporary variations caused by solar activity or other external factors.
When to Update Declination Values
For most recreational navigation, updating declination values every few years is sufficient. However, in areas with rapid secular variation or for professional applications, annual updates may be necessary. The calculator shows the annual change rate, which can help determine how frequently updates are needed for your specific location and application.
Alternative Navigation Methods
While magnetic declination is important for compass navigation, modern technology offers alternatives. GPS navigation eliminates the need for magnetic declination corrections, and digital compasses can be automatically calibrated. However, understanding magnetic declination remains important for backup navigation systems and for interpreting historical maps and documents.

Best Practices for Navigation:

  • Always verify declination values with local sources when possible
  • Account for declination in both map-to-compass and compass-to-map conversions
  • Update declination values regularly, especially in areas with rapid changes
  • Use multiple navigation methods for redundancy in critical situations