Magnetic Declination Calculator

Magnetic declination, also called magnetic variation, is the horizontal angle between true geographic north and the direction indicated by a magnetic compass. An easterly declination means magnetic north lies east of true north, while a westerly declination means it lies west. Because maps and geographic bearings usually reference true north, navigators must apply declination when transferring a compass bearing to a map or converting a map course into a compass heading. Earth's magnetic field is generated by moving conductive material in the outer core. Its magnetic poles do not coincide with the geographic poles, and they drift over time. Declination therefore depends on latitude, longitude, altitude, and date. It can be near zero along agonic lines, modest in many populated regions, and very large close to the magnetic poles. Local iron deposits, vehicles, buildings, electrical equipment, and the compass itself can introduce additional deviation that a global field model cannot predict. This calculator provides a transparent centered-dipole estimate. It models magnetic north near 86.5 degrees north and 164 degrees east in 2025, with a small annual drift, then calculates the initial great-circle bearing from the entered location toward that pole. The angular difference from geographic north is reported as east or west declination. This simplified geometry is deterministic and useful for learning how location and pole movement affect compass direction, but it does not include the many spherical-harmonic coefficients used by the World Magnetic Model. To use declination, follow the convention printed on the map or required by the navigation method. A common mnemonic is that an easterly declination is added when converting a magnetic bearing to true, while a westerly declination is subtracted. The inverse operation is used when converting true to magnetic. Sign conventions can vary among instruments and software, so always verify the convention rather than relying only on a mnemonic. For hiking practice, classroom demonstrations, and rough orientation, the estimate illustrates the relevant relationship. For marine, aviation, surveying, military, emergency, or other safety-critical work, obtain current values from an official World Magnetic Model or national geophysical service using the exact date, altitude, and coordinates. Check the map's publication date because an old printed declination can be materially different today. Calibrate the compass away from metal and electrical interference, and remember that magnetic declination correction does not compensate for local compass deviation.