Use this NOAA-style magnetic declination calculator to estimate magnetic variation for your location and date. Enter latitude, longitude, and date, then click Calculate.
Heading Converter
Declination uses the convention: East = positive, West = negative.
What Is Magnetic Declination?
Magnetic declination (also called magnetic variation) is the angle between true north (geographic north) and magnetic north (where a compass points). This angle changes depending on location and time. In some places your compass points several degrees east of true north; in others it points west.
If you navigate using maps, a sighting compass, aviation charts, marine charts, or GPS waypoints, declination matters. A small mismatch can create large position errors over long distances.
Why Use a NOAA Magnetic Declination Calculator?
The NOAA geomagnetic tools are based on accepted geomagnetic models (such as the World Magnetic Model). These models are updated because Earth’s magnetic field drifts over time. Using a date-aware calculator helps keep bearings accurate for:
- Backpacking and wilderness navigation
- Land surveying and field mapping
- Aviation and marine route planning
- Drone mission planning and geospatial work
How to Use This Calculator
Step 1: Enter Coordinates
Use decimal degrees. North latitude is positive; south is negative. East longitude is positive; west is negative.
Step 2: Pick the Date
Declination changes year to year, so always choose the observation date when possible.
Step 3: Calculate
The tool first attempts a NOAA-based query. If unavailable, it provides a local fallback estimate so you still get a usable value quickly.
True vs Magnetic Bearing Formulas
Use these practical formulas (East positive, West negative):
- Magnetic = True − Declination
- True = Magnetic + Declination
Example: If true heading is 100° and declination is +8° (East), magnetic heading is 92°.
| Scenario | Declination | Input | Result |
|---|---|---|---|
| Convert True to Magnetic | +10° E | True 250° | Magnetic 240° |
| Convert Magnetic to True | -6° W | Magnetic 40° | True 34° |
| Convert True to Magnetic | -12° W | True 90° | Magnetic 102° |
Tips for Better Accuracy
- Use precise coordinates from GPS when possible.
- Set the correct date, especially for old surveys or future plans.
- For critical work, cross-check with official NOAA tools before final submission.
- Remember local magnetic interference (vehicles, power lines, steel objects) can affect compass readings in the field.
Frequently Asked Questions
Is magnetic declination the same everywhere?
No. It varies significantly by location and can differ by dozens of degrees from one region to another.
Does declination stay constant?
No. Earth’s magnetic field slowly changes, so declination values drift over time.
What if NOAA service is unavailable?
This page includes a built-in local fallback estimate, but for mission-critical applications always verify with official NOAA/NCEI products.
Bottom Line
If you use a compass with maps, waypoints, or geospatial data, declination is not optional. A NOAA magnetic declination calculator helps you align true and magnetic directions so your navigation stays accurate and repeatable.