Magnetic Declination Converter

Magnetic declination is the angle between true north and magnetic north.

The conversion:

• True Bearing = Magnetic Bearing + Declination
• Magnetic Bearing = True Bearing - Declination

East declination is positive, West declination is negative.

Example declination values (approximate, they change over time):

• New York, USA: -13 deg (west declination)
• London, UK: -1 deg (west declination)
• Los Angeles, USA: 12 deg (east declination)
• Sydney, Australia: 12 deg (east declination)
• Tokyo, Japan: -7 deg (west declination)

Important notes:

• Declination changes slowly over time (about 0.1 deg per year in many places).
• Always use the current declination for your specific location.
• NOAA provides current declination data at ngdc.noaa.gov.

Declination is the correction that reconciles a compass with a map. The needle points to the magnetic pole, but maps are drawn to the geographic (true) pole, and the angle between them depends entirely on where you stand. Near the agonic line, where the two norths happen to align, declination is zero; far from it, it can exceed 20 degrees, enough to put you well off course over a few miles.

The catch that surprises people is that declination isn’t fixed. The magnetic pole wanders, so the correction drifts over years, which is why good topographic maps print both the declination and the date it was measured; an old map’s value can be stale. For short walks the error is negligible, but for serious backcountry navigation you set your compass’s declination adjustment to the current local value, then read bearings straight off the map without redoing the math each time.