How to use it
- Set the start point and the destination: search, use your location, or click the map.
- Read the true bearing, the magnetic bearing and the distance. The dashed line at the start points true north.
- Drag either pin to change the points. Press Swap to get the reverse bearing.
5 practical uses
- Set a compass course for a hike, a sail or a flight leg.
- Aim a directional antenna, a satellite dish or a solar array.
- Describe a direction in a report: "the mast lies 235° from the house".
- Work out the back bearing to find your way home.
- Check the direction to Mecca, a landmark or a distant peak.
The maths behind it
The initial bearing from (φ₁, λ₁) to (φ₂, λ₂) is θ = atan2(sin Δλ cos φ₂, cos φ₁ sin φ₂ − sin φ₁ cos φ₂ cos Δλ), normalised to 0 to 360°. The final bearing is the initial bearing of the reverse path plus 180°. The magnetic bearing is the true bearing minus the declination from the World Magnetic Model at the start point.
True and magnetic
The true bearing is measured from true north, the direction of the North Pole, and is what a map gives. A compass points at magnetic north, which is off by the magnetic declination of the place; the magnetic bearing is the true bearing minus the declination (east declination is positive). It is computed from the World Magnetic Model 2025 for today's date at the start point. See the magnetic declination tool for the details.
On a long path the bearing changes as you go: the initial bearing is the one to set off on, the final bearing the one you arrive on, and the back bearing is the direction from the destination back to the start.