Calculating True North from Magnetic North

Q. What is True North?

A. True North is the geographic North Pole. It is located at 90° North latitude and all lines of longitude converge at the pole. The Earth's axis connects the north and south poles. The Earth's axis is the line around which the Earth rotates. The North Pole is approximately 450 miles (725 km) north of Greenland in the middle of the Arctic Ocean.

Q. What is Magnetic North?

A. Magnetic North is the magnetic north pole. It is the focus of the planet's magnetic field and is the point magnetic compasses point toward. Unlike the geographic North Pole, the magnetic north pole moves (even daily). It moves approximately 9 miles (15 km) each year. It is presently located about 1000 miles (1600 km) south of the geographic North Pole at 78° 18' North and 104° West (southwest of Nunavut in Northern Canada).

Q. How do you calculate True North from Magnetic North?

A. The difference between Magnetic North and True North is called the variation. To convert magnetic readings to true, you need to find the variation for your particular location. Maps such as U.S. Geological Survey maps, aviation charts and marine charts all list the variation. Because variation changes from location to location, you need to get a map for your area. Variation is listed in terms of degrees east or west. If it is east variation, you subtract the number of degrees from the magnetic direction to obtain the true direction. If it is west variation, you add the number of degrees to the magnetic direction to obtain the true direction.

Note: If you use a compass to determine Magnetic North in relation to the building line that you plan to orient at 90° to the perpendicular in your drawing, and factor in your local variation, you should easily be able to calculate True North in relation to your plan.