Magnetic Declination Calculator
Free calculate the angle between true north and magnetic north for navigation. Get instant, accurate results with our easy-to-use calculator.
Input Parameters
Degrees (e.g., 40.7128 for New York)
Degrees (e.g., -74.0060 for New York)
Note: This calculator provides an approximation. For precise values, use NOAA's magnetic field calculator with current date.
Results
Enter location to calculate
What is Magnetic Declination?
Magnetic declination (also called magnetic variation or compass variation) is the angle between true north (geographic north) and magnetic north (the direction a compass points). This angle varies by location and changes over time.
Magnetic declination is essential for accurate navigation. A compass points to magnetic north, but maps and GPS use true north. The difference can be significant - in some locations, declination exceeds 20°, causing substantial navigation errors if not corrected.
Declination changes over time due to the Earth's magnetic field shifting. It also varies with location - near the magnetic poles, declination can be very large. For precise navigation, always use current declination values from authoritative sources like NOAA.
Magnetic Declination
Convention:
- • Positive declination (East): Magnetic north is east of true north
- • Negative declination (West): Magnetic north is west of true north
- • Zero declination: Magnetic and true north align (agonic line)
Note: Declination varies with:
- • Geographic location (latitude and longitude)
- • Time (secular variation - changes over years)
- • Local magnetic anomalies
How to Use
-
1
Enter your location
Input latitude and longitude in decimal degrees. Use N/S for latitude, E/W for longitude.
-
2
Get declination value
The calculator provides an approximation based on location. For precise values, consult NOAA or other authoritative sources.
-
3
Apply to navigation
Add declination to compass reading to get true bearing, or subtract from true bearing to get compass reading.
Practical Examples
Example 1: New York City
Location: 40.7°N, 74.0°W. Typical declination: ~-13° (West).
Solution:
Magnetic north is 13° west of true north
To get true bearing: add 13° to compass reading
Example 2: London, UK
Location: 51.5°N, 0.1°W. Typical declination: ~+1° (East).
Solution:
Magnetic north is 1° east of true north
Small declination - minimal correction needed
Applications
Navigation
Converting between compass bearings and true bearings for accurate navigation using maps and compasses.
Surveying
Correcting compass readings for accurate land surveys, property boundaries, and construction layout.
Outdoor Activities
Hiking, orienteering, and wilderness navigation where accurate compass use is critical for safety.
Education
Teaching navigation, understanding Earth's magnetic field, and learning about geomagnetism.
Frequently Asked Questions
Why does declination change over time?
Earth's magnetic field is generated by the liquid outer core and shifts over time. The magnetic poles drift, causing declination to change. Typical rates: 0.1-0.2° per year in most locations.
How do I correct for declination?
If declination is West (negative): add it to compass reading to get true bearing. If East (positive): subtract from compass reading. Or: True = Magnetic + Declination.
What is the agonic line?
The agonic line is where declination = 0° (magnetic and true north align). It currently runs through parts of North America. Locations on this line need no correction.
Can declination be very large?
Yes! Near magnetic poles, declination can exceed 90°. In some locations (like parts of Alaska), declination exceeds 20°. Always check local values for accurate navigation.
Where can I get accurate declination values?
NOAA's National Centers for Environmental Information (NCEI) provides authoritative magnetic field calculators. Many GPS devices and mapping apps also display current declination values.