True to Magnetic Bearing Calculator
A true bearing is measured from geographic north; a magnetic bearing is what your compass shows, measured from magnetic north. The difference at any place is the magnetic declination, which drifts with location and time, so it cannot be hardcoded. Look up your current declination with the NOAA World Magnetic Model calculator, enter it here with east positive and west negative, and this tool converts your true bearing to a magnetic bearing (and back), normalized to the 0 to 360 degree range.
Bearing conversion formula
Magnetic bearing = true bearing - declination
True bearing = magnetic bearing + declination
Declination: east positive, west negative
Normalize result to 0..360 degrees
Subtracting an east (positive) declination gives a smaller magnetic number, because magnetic north sits east of true north. The reverse conversion adds the declination back.
Bearing context
- True north is geographic; magnetic north is where a compass points.
- Declination changes with location and time, so look it up for your date and place.
- East declination is positive, west is negative (NOAA convention).
- NOAA's World Magnetic Model provides the official declination values.
- Aviation and marine charts print local variation for the same reason.
Bearing conversion: frequently asked questions
What is the difference between true and magnetic bearing?
A true bearing is measured from geographic (true) north, the direction of the North Pole. A magnetic bearing is measured from magnetic north, where a compass points. The angle between them at your location is the magnetic declination (also called magnetic variation).
How do I convert true bearing to magnetic bearing?
Subtract the declination from the true bearing when declination is east (positive), or add it when declination is west (negative). With east declination positive, the rule is magnetic bearing equals true bearing minus declination, then normalized to 0 to 360 degrees.
Why isn't the declination built in?
Magnetic declination changes with both location and time as the Earth's magnetic field drifts, so there is no single correct value. Look up your current declination from the NOAA World Magnetic Model calculator and enter it here. Treating it as a user input keeps the result accurate and honest.
What sign convention does declination use?
East declination is positive, west is negative, matching the NOAA and aeronautical convention. For example, a declination of plus 10 degrees means magnetic north lies 10 degrees east of true north, so a true bearing converts to a smaller magnetic bearing.
Where do I find my magnetic declination?
NOAA's National Centers for Environmental Information publishes the World Magnetic Model and an online declination calculator. Enter your latitude, longitude and date there to get the current declination, then bring that number into this calculator.
Official sources
- NOAA NCEI World Magnetic Model: World Magnetic Model.
- NOAA geomagnetic calculators: Magnetic field calculators.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.