Magnetic Declination Calculator
Find the angle between true north and magnetic north for any location and date.
Major Global Locations
New York, USA
Declination: -12.5°
Location: 40.7128°, -74.006°
Seattle, USA
Declination: 14.9°
Location: 47.6062°, -122.3321°
Denver, USA
Declination: 7.5°
Location: 39.7392°, -104.9903°
London, UK
Declination: 1.2°
Location: 51.5074°, -0.1278°
Cape Town, South Africa
Declination: -26.8°
Location: -33.9249°, 18.4241°
Mumbai, India
Declination: 0°
Location: 19.076°, 72.8777°
Tokyo, Japan
Declination: -7.9°
Location: 35.6762°, 139.6503°
Sydney, Australia
Declination: 12.8°
Location: -33.8688°, 151.2093°
Navigation Guide
Adjusting for Declination
Map to compass (true bearing to magnetic bearing): magnetic bearing = true bearing − declination (east positive, west negative).
Compass to map (magnetic bearing to true bearing): true bearing = magnetic bearing + declination.
Memory aid for map to compass: “East is least, west is best” — subtract east declination, add west declination.
Example
Map (true) bearing is 90° and declination is 10° West (−10°): to set your compass, 90° − (−10°) = 100°.
Map (true) bearing is 90° and declination is 10° East (+10°): to set your compass, 90° − 10° = 80°.
Historical Changes
Magnetic declination values change over time due to the movement of the Earth's magnetic poles. The rate of change can be up to 1° every five years in some locations.
Key Changes (London)
- 2000: -3.21°
- 2010: -2.03°
- 2020: -1.42°
Common Mistakes to Avoid
Ignoring Local Variations
Declination can vary significantly over short distances. Always check local values rather than using regional averages.
Using Outdated Values
Magnetic declination changes over time. Using old maps or guides without checking current values can lead to navigation errors.
Incorrect Adjustment Direction
Adding when you should subtract (or vice versa) can double your error. Always double-check your calculations.
Frequently Asked Questions
What is magnetic declination?
Magnetic declination is the angle between true north (the direction to the geographic North Pole) and magnetic north (where a compass needle points). It is written in degrees east or west, or as a positive (east) or negative (west) number, and it varies by location and drifts slowly over time.
Is east declination positive or negative?
East declination is positive and west declination is negative. For example, 12.5° W is written as −12.5°.
How often should I check declination values?
Check it before any trip where you rely on a compass, and at least once a year -- in some regions it changes by 0.2 to 0.3 degrees per year.
How do I adjust my compass for declination?
To go from a true (map) bearing to a compass bearing, subtract east declination or add west declination: magnetic bearing = true bearing − declination. To go the other way, true bearing = magnetic bearing + declination. Many modern compasses have an adjustable declination scale to make this correction automatic.
Do I need declination if I use GPS?
GPS headings are usually true bearings, so no -- but if you compare a GPS or map bearing with a magnetic compass, you must apply declination.