🧠Magnetic Declination Calculator
Calculate magnetic declination (magnetic variation)
Bearing relative to true north (0-360°)
Bearing relative to magnetic north (0-360°)
How to Use This Calculator
Enter True Bearing
Input the bearing relative to true (geographic) north in degrees (0-360°). True north points to the geographic North Pole.
Enter Magnetic Bearing
Input the bearing relative to magnetic north in degrees (0-360°). Magnetic north is where a compass points and varies by location.
Calculate
Click the "Calculate Magnetic Declination" button to get the magnetic declination in degrees. Positive values indicate east declination, negative values indicate west declination.
Formula
Declination = True Bearing - Magnetic Bearing
Where:
- Declination = Magnetic Declination (degrees, °)
- True Bearing = Bearing relative to true north (degrees, °)
- Magnetic Bearing = Bearing relative to magnetic north (degrees, °)
Conversion Formulas:
True Bearing = Magnetic Bearing + Declination
Magnetic Bearing = True Bearing - Declination
Example Calculation:
If true bearing is 45° and magnetic bearing is 50°:
Declination = 45° - 50° = -5° (5° West)
Note: East declination is positive (magnetic north east of true north), west declination is negative. Declination varies by location and changes over time.
About Magnetic Declination Calculator
The Magnetic Declination Calculator determines the angular difference between true (geographic) north and magnetic north at a specific location. Magnetic declination, also called magnetic variation, varies by location and changes over time due to Earth's shifting magnetic field. Understanding declination is essential for accurate navigation using compasses and maps.
When to Use This Calculator
- Navigation: Convert between true and magnetic bearings for accurate navigation
- Surveying: Account for magnetic declination in land surveying
- Orienteering: Correct compass readings for map navigation
- Aviation: Convert between true and magnetic headings
- Maritime Navigation: Calculate compass corrections for sea navigation
Why Use Our Calculator?
- ✅ Quick Calculation: Instantly determine magnetic declination from bearings
- ✅ Bidirectional: Convert between true and magnetic bearings
- ✅ Navigation Essential: Critical for accurate compass and map navigation
- ✅ Free Tool: No registration or payment required
- ✅ Educational: Learn about Earth's magnetic field and navigation
Common Applications
Map Navigation: Convert magnetic compass readings to true bearings for use with maps oriented to true north. Maps typically show true north, while compasses point to magnetic north. The declination allows accurate conversion between the two systems, essential for backcountry navigation and orienteering.
Aviation and Maritime: Navigators use magnetic declination to convert between true headings (relative to geographic north) and magnetic headings (what compasses show). Flight plans often use true headings, while pilots navigate using magnetic compasses, requiring declination corrections.
Surveying and Mapping: Land surveyors account for magnetic declination when using magnetic compasses for measurements. Historical surveys may have used magnetic north, requiring declination correction for modern mapping systems based on true north.
Tips for Best Results
- Declination varies by location - check local declination charts or online tools
- Declination changes over time (typically 0.1-0.2° per year) - use current values
- East declination: add to magnetic bearing to get true bearing
- West declination: subtract from magnetic bearing to get true bearing
- Along the agonic line, declination is zero (magnetic and true north align)
Frequently Asked Questions
What is magnetic declination?
Magnetic declination (also called magnetic variation) is the angle between true (geographic) north and magnetic north. It varies by location and changes over time. Positive values indicate magnetic north is east of true north, negative values indicate it's west.
Why does magnetic declination vary by location?
The Earth's magnetic field is not perfectly aligned with the geographic poles. The magnetic north pole is currently in northern Canada, while the geographic north pole is in the Arctic Ocean. The angle between these two poles varies depending on your location on Earth's surface.
Does magnetic declination change over time?
Yes, magnetic declination changes slowly over time (typically 0.1-0.2° per year) as Earth's magnetic field shifts. The magnetic poles are moving, and the field itself changes. Always use current declination values for accurate navigation. Historical declination values differ significantly from current ones.
How do I find the declination for my location?
Many online tools and apps provide current magnetic declination based on your GPS coordinates. Topographic maps often show declination values. NOAA (in the US) and similar agencies provide declination calculators and charts. Always use current values, as declination changes over time.
What is the agonic line?
The agonic line is where magnetic declination is zero - magnetic north and true north align. Currently, it runs roughly from the Great Lakes through the Gulf of Mexico. Locations east of the agonic line have west declination (negative), locations west have east declination (positive).
How do I convert between true and magnetic bearings?
To convert magnetic to true: True = Magnetic + Declination (if east, add; if west, subtract). To convert true to magnetic: Magnetic = True - Declination. Remember: east declination is positive, west is negative. For example, with 10° east declination: True = Magnetic + 10°.