Magnetic Declination Calculator

Magnetic declination is the angle between true north (geographic north pole) and magnetic north (where a compass needle points). This angle varies depending on your location on Earth and changes slowly over time due to shifts in Earth's magnetic field.

First, find your magnetic declination using this calculator by entering your latitude and longitude. Then, on an adjustable compass, rotate the declination adjustment dial by the number of degrees shown. If declination is East (positive), rotate the dial East; if West (negative), rotate it West. Consult your compass manual for the specific adjustment method.

East declination (positive value) means magnetic north is to the right of true north. West declination (negative value) means magnetic north is to the left of true north. For navigation, if declination is East you subtract the value from your compass bearing to get a true bearing; if West, you add it.

On an iPhone, open the Compass app and scroll down to see your latitude and longitude. On Android, open Google Maps, tap and hold your current location, and the coordinates will appear at the top of the screen. You can also use GPS apps like 'GPS Coordinates' for a dedicated readout.

Yes, magnetic declination changes gradually each year as Earth's magnetic field slowly shifts. The annual change is typically small (a few minutes of arc per year) but can accumulate significantly over decades. Always use the current year when looking up declination for navigation, and recheck every few years if you use the same map.

Maps are oriented to true north, but compasses point to magnetic north. If you don't account for declination, your compass bearing will be off by the declination angle, which can lead you significantly off course over long distances. In areas with 10–20° of declination, the error can be hundreds of meters per kilometer traveled.

Magnetic declination varies widely across the US. The East Coast typically has West (negative) declination of around 10–15°, while the West Coast has East (positive) declination of around 10–15°. There is a line of zero declination (the agonic line) that roughly runs through the middle of the country. Enter your specific coordinates above to get the precise value for your location.

This calculator uses an approximation model based on known magnetic field behavior and is suitable for general navigation and compass setting purposes. For precise scientific or surveying work, use NOAA's World Magnetic Model (WMM) tool, which is updated every five years and provides certified accuracy.