Magnetic Declination Calculator - True and Magnetic Bearing

A magnetic declination calculator converts the heading your compass needle points to into the heading you read off a true-north map, and vice versa. Magnetic declination is the signed angle between magnetic north and true north at your location, and the calculator adds or subtracts that angle from any bearing you give it. East declination is positive and west declination is negative, so one signed value aligns a compass with a map anywhere on Earth.

• • Land navigation with a paper map and compass: Convert a magnetic compass reading into the true bearing to follow on a topographic map and confirm the back azimuth when you retrace your steps.
• • Marine piloting: Apply the local magnetic variation from a NOAA or admiralty chart so the heading you steer matches the chart's true bearing.
• • Drone and survey work: Correct raw magnetometer headings to true north before logging waypoints or stitching survey grids.
• • Classroom and field exercises: Show students how magnetic north drifts from true north by tens of degrees.

Magnetic declination varies by location and year, so pilots and surveyors refresh their value from the current World Magnetic Model release every five years.

When you have two GPS coordinates and need the compass bearing between them rather than the reverse correction, the azimuth calculator returns the bearing, quadrant, and great-circle distance from any pair of latitude/longitude points, which is the coordinate-side companion to this compass-to-map conversion.

The calculator reads the compass bearing, the declination magnitude, and the east or west direction, applies the NOAA NCEI sign convention internally, normalizes the result into the 0 to 360 range, and reports the true map bearing alongside a back-bearing and reciprocal bearing check.

• Magnetic bearing: Compass heading in degrees clockwise from magnetic north, from 0 to 360.
• Declination value: Local declination magnitude in degrees, taken from a NOAA NCEI lookup, an aviation database, or a World Magnetic Model grid.
• Declination direction: East (positive) or West (negative). The calculator multiplies the magnitude by plus or minus one before applying it.
• True bearing: Heading on a true-north map, equal to the magnetic bearing plus the signed declination, normalized to 0 to 360 degrees.
• Reciprocal true bearing: The back azimuth in true degrees, equal to the true bearing plus 180 and normalized, used to confirm the return path.

The calculator normalizes each output to 0 to 360 degrees so wrap-around cases such as magnetic 350 with a 20 degree west declination still produce a clean true bearing of 330 degrees.

It echoes the back magnetic bearing as a sanity check: re-deriving magnetic from true should return the original compass reading, which catches sign errors before you trust the conversion.

According to the British Geological Survey Models and Compass Variation page, the World Magnetic Model is produced jointly with NOAA's National Centers for Environmental Information and is the standard model in UK and US Department of Defense navigation systems, revised every five years (WMM2025 is valid through 2030.0).

For the other navigational correction pilots apply on long flights, the coriolis effect calculator returns the latitude-dependent deflection from Earth's rotation that surveyors, snipers, and long-range pilots must compensate for when plotting a course.

Four ideas cover every number the magnetic declination calculator reports.

These four definitions cover every output the result panel shows and explain why the same formula aligns compass and map in any region.

For pilots, the heading kept on a compass rose is a magnetic bearing until the moment of correction; the bank angle calculator solves the related applied-angle problem of how much an aircraft must bank to hold a coordinated turn at a given speed and radius.

Five short steps move you from a compass reading to a true map bearing and a back-bearing check.

1. 1 Enter the magnetic bearing: Type the compass heading in degrees clockwise from magnetic north. Most hand-held compasses already print this value, and the calculator accepts 0 to 360 degrees.
2. 2 Look up the local declination: Find the local declination for your latitude, longitude, and date from a magnetic field lookup service, or read the declination printed on the margin of a current topographic map or aviation chart.
3. 3 Enter the declination magnitude: Type the absolute value of the declination in degrees. Do not add a sign here; the next step controls the sign.
4. 4 Pick East or West direction: Choose East to apply the value as positive or West to apply it as negative. The calculator mirrors the NOAA NCEI convention so the same number works as either a positive or negative correction.
5. 5 Read true, back, and reciprocal bearings: Use the true bearing on the map, the back magnetic bearing as a sanity check, and the reciprocal true bearing when you want the reverse direction along the same line.

Hiking in the Pacific Northwest with a 16 degree east declination, a compass reading of 270 returns true bearing 286 and reciprocal true bearing 106, so you follow 286 degrees on the topo map and turn around at 106 on the compass.

For the related conversion when the bearing is logged in degrees-minutes-seconds rather than decimal degrees, the decimal to minutes degrees calculator translates any decimal bearing into DMS format and back, which is the notation printed on most USGS quadrangles and sectional aeronautical charts.

A dedicated magnetic declination calculator removes the sign and wrap-around errors of a hand calculation in the field.

• • Applies the official NOAA NCEI sign convention: East declination is positive and west declination is negative so the same formula matches aviation, marine, and land navigation references.
• • Handles wrap-around automatically: Bearings near 0 or 360 and large declination values wrap inside 0 to 360 degrees, so the output always fits a real compass dial or map protractor.
• • Returns a back-bearing sanity check: The back magnetic bearing and reciprocal true bearing panels let you confirm the conversion by re-deriving the original input, which catches sign or magnitude mistakes before you trust the result.
• • Reports the offset magnitude and direction together: A separate magnetic-versus-true offset row shows the absolute correction and the East or West label in one place, which is the exact information printed on a topographic map margin.
• • Works for any region on Earth: The formula is generic, so the calculator handles a Seattle sixteen degrees east, a Boston sixteen degrees west, and the small declinations near the agonic line without code changes.

This calculator is best for a single bearing correction at a time. For batch waypoint planning, repeat the calculation for each course leg rather than averaging declination across a long route.

When the route is long enough that the surface of the Earth matters, the great circle calculator returns the shortest-path bearing and distance between two coordinates using the haversine formula, which pairs with this compass correction when you are plotting an inter-city or trans-oceanic heading.

Three inputs determine the answer, and three caveats tell you when to expect the real compass reading to differ from the model.

• • Local magnetic anomalies from ore deposits, steel structures, or power lines can deflect the compass needle by several degrees, so treat one bearing as a starting point and re-check away from obvious interference.
• • Secular variation moves declination by a few tenths of a degree per year, so values older than five years are best re-pulled from the current model.
• • Compass tilt, magnetic dip near the poles, and uncalibrated smartphone magnetometers add error that the signed-declination formula does not correct; use a sighting compass or a calibrated sensor when sub-two-degree accuracy matters.

The back-bearing row is useful in the field: if the recomputed magnetic reading differs from the original compass value, suspect one of these error sources before trusting the true bearing.

According to the British Geological Survey Models and Compass Variation page, compass variation (the same quantity as magnetic declination) is the angle required to convert between a magnetic and a true or grid bearing.

As published by the British Geological Survey WMM Calculator, the World Magnetic Model returns declination as D in degrees east with positive values for east declination and negative values for west, using the WMM2025 release.

When you also need to convert the corrected bearing into UTM coordinates for a survey grid or a GIS database, the lat long to UTM calculator returns the zone, easting, and northing from any latitude/longitude pair, which is the next conversion in the same survey workflow.