Magnetic Declination Formula
Convert between true north and magnetic north.
Essential for accurate compass navigation anywhere on Earth.
The Formula
True Bearing = Magnetic Bearing + Declination
Magnetic declination is the angle between true north (geographic) and magnetic north (where the compass points). It varies by location and changes slowly over time as Earth's magnetic field shifts.
Variables
| Symbol | Meaning |
|---|---|
| True Bearing | Direction relative to true (geographic) north |
| Magnetic Bearing | Direction shown on a magnetic compass |
| Declination | Angle between true north and magnetic north (positive = east, negative = west) |
Example 1
Your compass reads 120° and the local declination is +10° East
True Bearing = 120° + 10°
True Bearing = 130°
Example 2
You need to travel on a true bearing of 45°. Local declination is -15° West.
Magnetic Bearing = True Bearing - Declination
Magnetic Bearing = 45° - (-15°) = 45° + 15°
Set your compass to 60°
When to Use It
Use the magnetic declination formula when:
- Navigating with a magnetic compass in the wilderness
- Converting between map bearings and compass readings
- Calibrating navigation instruments
- Working with nautical or aeronautical charts