Magnetic Declination Calculator
The magnetic declination calculator converts between true bearings (referenced to geographic north) and magnetic bearings (referenced to magnetic north). Enter a bearing and the magnetic declination for your location (positive for east declination, negative for west) to get both conversions. Look up the current declination for your location from NOAA's National Centers for Environmental Information at ngdc.noaa.gov, as it changes with time and location. This conversion is essential for accurate compass navigation, land surveying, and map reading.
Declination conversion formula
Magnetic bearing = (True bearing - Declination + 360) mod 360
True bearing = (Magnetic bearing + Declination + 360) mod 360
Declination is positive for east (magnetic north is east of true north) and negative for west. Results are always normalized to the 0-360 degree range.
US magnetic declination reference values (approximate, 2025)
- New York City: approximately -13 degrees (west declination). Magnetic north is west of true north.
- Chicago: approximately -2 degrees. Very close to zero (agonic line passes nearby).
- Los Angeles: approximately +11 degrees (east declination). Magnetic north is east of true north.
- Seattle: approximately +15 degrees east declination.
- Always use current values from NOAA NCEI for accurate navigation, as values drift over time.
Magnetic declination calculator: frequently asked questions
What is magnetic declination?
Magnetic declination is the angle between true geographic north and magnetic north at a specific location. It varies by location and changes slowly over time as Earth's magnetic field shifts. East declination means magnetic north is east of true north; west declination means it is west.
How do I find the magnetic declination for my location?
NOAA's National Centers for Environmental Information (NCEI) publishes the World Magnetic Model and provides an online declination calculator at ngdc.noaa.gov. Enter your location and the date to get the current declination value with annual rate of change.
How do I convert a true bearing to a magnetic bearing?
Magnetic bearing = True bearing - Declination (east positive, west negative). Or using the mnemonic: 'East is least, West is best.' East declination: subtract from true to get magnetic. West declination: add to true to get magnetic.
How do I convert a magnetic bearing to a true bearing?
True bearing = Magnetic bearing + Declination (east positive, west negative). For east declination: add to magnetic to get true. For west declination: subtract from magnetic to get true. Results are normalized to 0-360 degrees.
How often does magnetic declination change?
Magnetic declination changes slowly, typically 0.1 to 0.3 degrees per year in the US, but can be higher near the magnetic poles. NOAA updates the World Magnetic Model every 5 years. Maps printed more than 10 years ago may show significantly outdated declination values.
Official sources
- NOAA National Centers for Environmental Information: NOAA Magnetic Declination Calculator.
- NOAA National Geodetic Survey: NGS geodetic tools and standards.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.