Bearing Calculator

What “bearing” actually means on Earth

A bearing is a compass direction expressed in degrees, measured clockwise from a reference north. Three flavours are in everyday use.

True bearing is measured from geographic (true) north — the rotational axis of the Earth. This is what this tool returns by default.

Magnetic bearing is measured from magnetic north — where the compass needle points. Magnetic north drifts over time and varies by location; the difference between true and magnetic is the magnetic declination.

Grid bearingis measured from the “up” direction of a map grid (e.g. UTM grid north). On most projections it differs from true north by a small amount called grid convergence.

How bearing drifts along a great-circle route

The diagram above traces the New York → Tokyo great-circle path. The arrows along the route show the heading at the start, midpoint, and arrival. The bearing rotates by roughly 150° across the 9,500 km flight.

The cause is geometry, not navigation error. Meridians of longitude converge at the poles, so a great-circle path that runs true to the east at the equator runs true to the south by the time it reaches the pole. Pilots and ship captains correct heading continuously along long routes — modern autopilots do this automatically.

True bearing versus magnetic bearing

A compass needle points to magnetic north, which is offset from true (geographic) north by the local magnetic declination. The declination changes with location and slowly drifts over time as Earth's magnetic field shifts.

The diagram above shows the conversion at New York — declination currently about 13° West, so a true bearing of 90° (due east) corresponds to a magnetic bearing of about 103°.

The conversion formula: magnetic = true − declination. East declination is positive; west declination is negative.

Coordinately uses the NOAA / NCEI World Magnetic Model 2025 (valid 2024-11-13 → 2029-11-13) to compute declination at any coordinate. The values shown in the bearing report above are evaluated at your two endpoints.

Back bearings (return-leg navigation)

The reciprocal of a bearing is its 180°-opposite — the direction from B back to A along the same great-circle path. The tool reports both back bearings (return initial = reciprocal of the original final; return final = reciprocal of the original initial).

For a pilot or sailor planning a round trip, the back bearings are the headings for the return leg. They are notsimply “the bearings minus 180°” — they account for the direction change along the path.

Ten ways bearing calculation gets used in production

Anywhere two coordinates have a meaningful direction between them, the bearing calculation is running. The ten cases below cover most of the real-world traffic.

1. Aviation flight planning (initial heading)

Pilots compute the initial bearing as the departure heading from runway alignment. ICAO Annex 5 and the FAA Pilot's Handbook of Aeronautical Knowledge both specify great-circle calculations on WGS-84.

Worked example: JFK (40.6413, -73.7781) → Narita (35.7720, 140.3929). Initial bearing ≈ 336° (NNW). Pilot files for departure heading 336° true; magnetic heading at JFK with ~13° W declination is ~349°.

2. Maritime great-circle sailing

Ship captains use bearings for course plotting on long open-water passages. Bowditch's American Practical Navigator (NGA Pub. 9) gives the spherical bearing formula.

Worked example: Cape Town (-33.9249, 18.4241) → Boston (42.3601, -71.0589). Initial bearing ≈ 308° (NW). The captain steers WNW on departure, with continuous correction across the Atlantic.

3. Amateur radio antenna pointing

Directional HF and VHF antennas (Yagi, log-periodic, satellite- tracking arrays) must be pointed at the remote station along the great-circle bearing. The ARRL Operating Manualpublishes “great-circle maps” for exactly this purpose; modern logging software computes the bearing live from station coordinates.

Worked example: Operator in Boulder, Colorado (40.0150, -105.2705) working a station in Perth, Australia (-31.9505, 115.8605). Initial bearing ≈ 287° (W) — antenna pointed roughly west.

4. Satellite ground-station antenna alignment

Earth-observation and communication satellites require ground stations to point antennas continuously as the satellite moves. The bearing to the sub-satellite point — the lat/lon directly below the satellite — is the azimuthal component of antenna aim.

Worked example: A station at ESA Kiruna (67.8569, 20.2256) tracking the ISS at sub-point (10.0, 30.0). Bearing from Kiruna ≈ 175° (S) — the antenna points south.

5. Hiking and orienteering navigation

Backcountry hikers carry a map + compass and convert between bearings on the map and headings on the compass. Map-side bearings are typically true (grid north on a topographic sheet); compass- side are magnetic. The hiker corrects with declination.

Worked example: Hiker at Mount Whitney trailhead (36.5872, -118.2403) heading toward the summit (36.5786, -118.2920). Bearing ≈ 264° (W); magnetic heading at ~11° E declination is ~253°.

6. Autonomous drone delivery

Delivery drones (Wing, Zipline, Amazon Prime Air) compute the great-circle bearing from current GPS fix to the delivery coordinate as the primary heading input to the flight controller. Re-computed every few seconds as the drone moves.

Worked example: Drone at warehouse (40.7484, -73.9857) heading to a delivery point (40.7580, -73.9855). Bearing ≈ 1° (N), distance ~1.1 km.

7. Photography golden-hour planning

Landscape photographers compute the bearing from a planned shoot location to the sun at golden hour to predict shadow direction and composition. Apps like PhotoPills and The Photographer's Ephemeris run this calculation live.

Worked example: Shoot at the Hollywood Sign (34.1341, -118.3215) at sunset, with the sun at azimuth ≈ 290° (WNW) — the bearing tells the photographer to face WNW for the sun-behind-camera composition.

8. Surveying and civil engineering

Cadastral surveys, pipeline alignment, and high-voltage transmission-line routing all use grid bearings on a local projected coordinate system (UTM, State Plane). The conversion from great-circle bearing to grid bearing — “grid convergence” — is documented in NGS Coordinate Conversion and Transformation Tool (NCAT).

Worked example: Pipeline alignment Houston (29.7604, -95.3698) to New Orleans (29.9511, -90.0715). Initial true bearing ≈ 87° (E). Grid convergence at this latitude and longitude is about −1.2°, so the grid bearing on UTM 15N is ~86°.

9. Search and rescue / military bearing-only fix

Bearing-only target localisation triangulates a target from two or more observers by intersecting the bearings each one reports. Used in SAR for distress beacons, by submarines for passive tracking, and in artillery direction-finding.

Worked example: Two listening stations at (40.0, -75.0) and (40.0, -74.0) both report a distress bearing. The intersection of those bearing lines locates the distress to within a small uncertainty ellipse.

10. Wind farm and turbine layout

Wind-turbine layouts are optimised against the prevailing wind direction. The bearing from each turbine to the next determines whether the downwind turbine sits in the upwind turbine's wake. Wake-loss models (Jensen, Frandsen) take bearing as a primary input.

Worked example: Hornsea offshore wind farm array, prevailing wind from ~230° (SW). Turbines aligned with their nearest-neighbour bearing 045°/225° are stacked in the wake; alignments perpendicular to that bearing minimise loss.

Choosing the right tool from the “between two points” family

Why a bearing might look wrong

• You're comparing it to the straight-line bearing on a Mercator map. A straight Mercator line is a rhumb line, not a great-circle path; rhumb-line bearings are constant but the path is longer than the geodesic.
• You're reading magnetic bearing on a true-bearing map (or vice-versa). Always check whether the source is true or magnetic. The conversion depends on declination at your location.
• You're near a magnetic pole. Declination becomes wildly variable and the WMM model is unreliable beyond about ±88° latitude. The geomagnetism library used here returns no value in those zones.
• You're computing for a return trip and forgot the back-bearing math.The return-trip initial bearing is not just “original − 180°” — it's the reciprocal of the original final bearing. The tool computes both for you.

Privacy and data-flow notes

Bearing computation runs entirely server-side from the lat/lon values you supply. Magnetic declination uses an embedded NOAA WMM model file with no external network call.

The only optional network traffic is the autocomplete on the From and To address inputs, proxied server-side via /api/geocode/suggest with Cache-Control: no-store per Mapbox ToS §19.2. Browser geolocation is button-triggered only and never automatic.