magnetic variation calculator

What Is Magnetic Variation?

Magnetic variation (also called magnetic declination) is the angular difference between True North and Magnetic North. Because Earth’s magnetic field is not perfectly aligned with the planet’s rotational axis, your magnetic compass does not point to true geographic north. That difference matters in aviation, marine navigation, surveying, and backcountry travel.

Why variation matters

• Charts and maps are usually based on true bearings.
• Compasses report magnetic bearings.
• If you skip conversion, route errors accumulate over distance.

Variation vs Deviation: Not the Same Thing

People often mix these up, but they are different corrections:

• Variation (Declination): Difference between true and magnetic north for your geographic location.
• Deviation: Error caused by magnetic influences inside your vessel/aircraft/vehicle (electronics, metal, wiring, etc.).

This calculator supports both so you can move between all three heading types: True, Magnetic, and Compass.

How This Calculator Works

Core equations used

With East as positive and West as negative:

• Magnetic = True − Variation
• True = Magnetic + Variation
• Compass = Magnetic − Deviation
• Magnetic = Compass + Deviation

All outputs are normalized to the 0° to less than 360° range.

Step-by-Step: Using the Tool

1) Enter what you already know

Type your heading and select whether it is true, magnetic, or compass.

2) Add local variation

Use your chart, sectional, or local declination source. Enter the value and direction (E/W).

3) Add deviation if applicable

If you have a deviation card (common in boats and aircraft), enter it. If not, leave it at zero.

4) Calculate and review all headings

The calculator returns true, magnetic, and compass headings at once, plus a short interpretation line.

Practical Example

Suppose your true course is 090°, local variation is 10°E, and your deviation is 2°W:

• Magnetic = 090 − 10 = 080°
• Compass = 080 − (−2) = 082°

You would steer approximately 082° compass to maintain a true course of 090° under those conditions.

Good Navigation Habits

• Verify the date of your declination source (variation changes over time).
• Re-check calculations on long legs or major course changes.
• Round consistently (for example, to the nearest degree) when flying or boating.
• Cross-check with GPS track and environmental factors (wind/current).

Final Thoughts

A magnetic variation calculator is simple, but the impact is huge: better route accuracy, safer operations, and fewer heading mistakes. Save this page for quick conversions whenever you need to move between true, magnetic, and compass references.