Magnetic Declination & Bearing Converter
Use this tool to estimate local magnetic declination from latitude/longitude and convert between true bearings and magnetic bearings.
1) Get Declination from Location
2) Convert Bearings
What Is Magnetic Declination?
Magnetic declination (also called magnetic variation) is the angle between true north (geographic north pole) and magnetic north (where your compass points). Because Earth’s magnetic field is uneven and slowly shifts over time, this angle changes by location and date.
If you’re working with a map, GPS route, or surveying line, declination helps you translate direction correctly between map-based bearings and compass-based bearings.
Why This Matters in the Real World
- Hiking and backpacking: Avoid course drift when using topo maps and compasses.
- Search and rescue: Coordinate map bearings and field bearings across teams.
- Forestry and land work: Keep transects and plots aligned with intended azimuths.
- Amateur navigation practice: Learn core compass conversion rules accurately.
How to Use the Calculator
Step 1: Estimate declination
Enter latitude, longitude, and date, then click Estimate Declination. The calculator attempts to query a live geomagnetic model, and if the service is unavailable, it applies a mathematical approximation so you can keep working.
Step 2: Convert a bearing
Choose a conversion type, enter your bearing, and click Convert Bearing. The tool uses this sign convention:
- East declination = positive (e.g., +8.4°)
- West declination = negative (e.g., -11.2°)
Conversion Rules (Simple and Reliable)
True to Magnetic
Magnetic Bearing = True Bearing − Declination
Example: True 100°, Declination +10° (East) → Magnetic 90°
Magnetic to True
True Bearing = Magnetic Bearing + Declination
Example: Magnetic 250°, Declination -8° (West) → True 242°
Declination Changes Over Time
A lot of people assume declination is a fixed number printed on a map forever. It isn’t. Earth’s magnetic field evolves continuously, so local declination can drift year by year. In some regions the annual change is tiny; in others it can be significant enough to matter over just a few years.
That’s why this calculator includes a date input. A 2026 declination can differ from a 2016 value even at the same coordinates.
Field Best Practices
- Record your declination and date in your field notebook.
- Confirm whether your compass has adjustable declination settings.
- Re-check declination when working in a new region.
- Normalize bearings to 0–360° to avoid arithmetic mistakes.
- When precision matters, validate with official regional geomagnetic data.
Quick FAQ
Is this calculator accurate everywhere?
It is practical for general use. When live geomagnetic model data is available, results are stronger. The fallback mode is an estimate and should not be used as the sole source for safety-critical navigation.
What does East or West declination mean?
East means magnetic north is east of true north (positive value). West means magnetic north is west of true north (negative value).
Can I enter any bearing value?
Yes. The calculator normalizes results automatically to the 0–360° range.
Final Note
Compass navigation is one of those timeless skills that rewards precision. A small correction at the start of your route can prevent a huge miss later. Use this magnetic declination calculator as your quick conversion companion, and always pair it with good map-reading habits.