# Magnetic Declination Calculator

Calculate approximate magnetic declination from coordinates. Convert compass bearings to true bearings. Simplified dipole model for navigation planning.

## What this calculates

Magnetic declination (or variation) is the angle between true north and magnetic north at your location. A compass needle points to magnetic north, not true north, so you need to know the declination to navigate accurately with a map and compass. East declination means magnetic north is east of true north; west declination means it is west.

## Inputs

- **Latitude** (°) — min -90, max 90 — Positive for North, negative for South.
- **Longitude** (°) — min -180, max 180 — Positive for East, negative for West.
- **Compass Bearing (optional)** (°) — min 0, max 360 — Optional: enter a magnetic compass bearing to convert to true bearing.

## Outputs

- **Magnetic Declination** (°) — Approximate angle between magnetic north and true north
- **Declination Direction** — formatted as text — East (positive) or West (negative) declination
- **True Bearing** (°) — Compass bearing corrected for declination
- **Approx. Grid Convergence** (°) — Approximate correction from true north to grid north

## Details

This calculator uses a simplified dipole model based on the approximate position of Earth's magnetic north pole (~80.7°N, 72.7°W as of 2025). For mission-critical navigation, use the official World Magnetic Model (WMM) or IGRF data from NOAA, which accounts for the full complexity of Earth's magnetic field.

The declination varies widely across the globe:

  - US East Coast: Roughly -10° to -15° (west declination)

  - US West Coast: Roughly +12° to +16° (east declination)

  - Central US: Near 0° along the agonic line

  - UK: Roughly -1° to +2°

  - Australia: Roughly +5° to +12° (east)

To convert a compass bearing to a true bearing:

True Bearing = Magnetic Bearing + Declination

Remember: "East is least, west is best." East declination is added, west declination is subtracted (it is already negative in this calculator).

Important: Magnetic declination changes over time as Earth's magnetic poles drift. The north magnetic pole moves roughly 40-50 km per year. Maps printed years ago may show outdated declination values. Always check current declination before a trip.

## Frequently Asked Questions

**Q: What is the difference between declination and inclination?**

A: Declination is the horizontal angle between true north and magnetic north. Inclination (or dip) is the vertical angle of the magnetic field. At the magnetic poles, inclination is 90 degrees (the compass needle tries to point straight down). At the magnetic equator, inclination is 0 degrees. Declination matters for compass navigation; inclination matters for some surveying instruments.

**Q: How accurate is this simplified model?**

A: The dipole approximation typically agrees with the full World Magnetic Model to within a few degrees at mid-latitudes, but can be off by 10 degrees or more near the poles, in areas with strong magnetic anomalies (like near iron deposits), or at high latitudes. For hiking and general planning it gives a reasonable estimate. For surveying, aviation, or military use, always use the official WMM or IGRF models from NOAA.

**Q: What is the agonic line?**

A: The agonic line is the imaginary line on Earth's surface where magnetic declination is zero, meaning a compass points to true north. In North America, the agonic line currently runs roughly through the central US from Louisiana north through Michigan. East of this line, declination is west (negative). West of it, declination is east (positive).

**Q: Does my phone compass already correct for declination?**

A: Most modern smartphones automatically correct for magnetic declination using their GPS position and a built-in magnetic model. When your phone shows a heading, it is usually the true heading. However, a traditional magnetic compass shows magnetic north and requires manual correction. Check your phone's compass app settings to confirm whether it shows true or magnetic north.

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Source: https://vastcalc.com/calculators/physics/magnetic-declination
Category: Physics
Last updated: 2026-04-08