Magnetic Declination Calculator
Align your compass correctly with this magnetic declination calculator!
True bearing87.5°magnetic 90° plus a declination of -2.5° — east declination is ADDED to get true, which is the direction people most often get backwards
Magnetic bearing90°what a compass needle points to, ignoring the instrument itself
Compass bearing90°what the instrument actually reads, after its own deviation from nearby iron and electronics
Declination-2.5° westthe angle between true north and magnetic north at your location. It varies with position AND drifts year by year, so a chart's value has an expiry date
The mnemoniceast is least, west is bestgoing from TRUE to MAGNETIC you subtract east declination and add west. Going the other way it reverses, which is exactly why the mnemonic causes as many errors as it prevents
Reverse bearing267.5°the back bearing, for retracing
Total correction applied-2.5°from compass reading to true bearing
Magnetic north is not the poleand it movesthe magnetic pole has drifted hundreds of kilometres in the past century and is currently moving at tens of kilometres a year. Declination therefore has to be looked up for a DATE as well as a place
The formula
true = magnetic + east declination; compass = magnetic − deviation
Three different norths
True north is the geographic pole. Magnetic north is where the field points, which differs by the declination — up to tens of degrees at high latitudes and near zero along the agonic line. Compass north is what your particular instrument reads, differing again by its deviation from nearby iron and electronics.
The sign convention is the usual source of error. East declination is added to a magnetic bearing to get true, and subtracted going the other way. The "east is least, west is best" mnemonic applies to converting TRUE to MAGNETIC and reverses for the opposite direction, which is why it causes about as many mistakes as it prevents.
Declination is not fixed. The magnetic pole has moved hundreds of kilometres over the past century and is currently drifting at tens of kilometres a year, so any chart value carries a date and an annual rate of change.