Magnetic Declination Calculator (WMM2025)

Computes the Earth's main magnetic field from the World Magnetic Model 2025, the model published by NOAA and the British Geological Survey that GPS receivers, smartphones and military navigation use. For a latitude, longitude, altitude and date it gives the declination (the angle from true north to magnetic north, positive to the east), the inclination or dip, the total intensity and its north, east and down components, and how fast declination, inclination and intensity are changing each year. Type a compass bearing to convert it between magnetic and true north, and above 55° of latitude the tool also gives the grid variation that polar navigation charts use. The synthesis reproduces all 100 of NOAA's official WMM2025 test values to a thousandth of a nanotesla. The model itself is not that precise about the real Earth: it describes the field from the core and ignores the crust, the ionosphere and magnetic storms, so the typical error in declination is about half a degree, and much more near iron ore bodies, volcanic rock, steel structures or vehicles. Close to the magnetic poles the horizontal field becomes too weak for a compass: below 6,000 nT the tool warns that compass readings degrade, and below 2,000 nT (the WMM blackout zone) declination is unreliable. WMM2025 is valid from 2025.0 to 2030.0 only; dates outside that span are refused rather than extrapolated.