Magnetic Declination Calculator
The National Oceanic and Atmospheric Administration has created this Magnetic Declination Calculator so that users can find magnetic north for any location on Earth. Magnetic declination is the angle between magnetic north (the direction the north end of a compass needle points) and true north.
To use the calculator you need to enter the latitude and longitude of a location (if it is for a US location you can just enter a zipcode). The results of the calculation are then shown by superimposing a compass rose on top of Google Maps (see screenshot above).
Magnetic Declination fluctuates over time. Using the Magnetic Declination Calculator it is possible to calculate the declination for any date from 1750 to the present.