Magnetic Declination Calculator
Find the difference between true north and magnetic north for navigation
Calculate Magnetic Declination
Latitude in decimal degrees (0-90°)
Longitude in decimal degrees (0-180°)
Height above WGS84 ellipsoid (GPS altitude)
Date for calculation (WMM2020 valid 2025-2029)
Magnetic Declination Results
Location: 0.0000°, 0.0000° at 0.000 km elevation
Compass correction: No correction needed
Date:
Navigation Instructions
Example: New York City
Location Data
Latitude: 40.7128° N
Longitude: 74.0060° W
Elevation: 10 meters above sea level
Date: September 19, 2025
Expected Results
Magnetic Declination: ~12.5° W
Meaning: Compass points 12.5° west of true north
Navigation: Add 12.5° to compass bearing for true bearing
Understanding Declination
Positive Declination
Compass needle points east of true north
Add declination to compass bearing
Negative Declination
Compass needle points west of true north
Subtract declination from compass bearing
Zero Declination
Compass points to true north
No correction needed
Applications
Compass navigation and orienteering
Topographic map reading
Aviation navigation
Hiking and wilderness navigation
Marine navigation
Antenna alignment
Understanding Magnetic Declination
What is Magnetic Declination?
Magnetic declination is the angular difference between true north (geographic north pole) and magnetic north (where compass needles point) at any given location on Earth. This difference varies by location and changes over time due to the movement of Earth's magnetic field.
Why Does It Matter?
- •Critical for accurate navigation with compass and map
- •Can vary up to 20+ degrees from true north
- •Essential for aviation and marine navigation
- •Required for precise surveying and mapping
World Magnetic Model
This calculator is based on the World Magnetic Model (WMM2020), developed by NOAA and the British Geological Survey. The model uses spherical harmonics to represent Earth's magnetic field and is updated every 5 years.
Current Model: WMM2020
Valid Period: 2025.0 - 2030.0
Accuracy: ±0.5° for most locations
Note: This calculator uses a simplified model for demonstration. For critical navigation, use official NOAA calculators or GPS devices.
How to Use Magnetic Declination
With a Compass
- 1. Find your magnetic declination
- 2. Take a compass bearing
- 3. Add/subtract declination for true bearing
- 4. Use true bearing with map
Finding True North
- 1. Hold compass level and steady
- 2. Turn until needle points to declination
- 3. North mark now points to true north
- 4. Take bearing to your destination