Flight Planning

Magnetic Variation Calculator

Convert between true and magnetic heading using the local variation — east is least, west is best.

Inputs

True course0–360°

VariationLocal magnetic variation

Result

Magnetic heading

100°

True 090° − (W) 10° · West is best (add)

True heading

If the entered course were magnetic

080°

Variation applied

East is least, West is best

10° W

Formula

Ref

East is least: magnetic = true − variation (E)
West is best: magnetic = true + variation (W)
Reverse the sign for magnetic → true

Worked example

Ref

True course 090°, variation 10° West.

1.West is best → ADD westerly variation to true.
2.Magnetic heading = 090° + 10° = 100°.
3.(Easterly variation would be subtracted — east is least.)

Magnetic heading 100° (variation 10° W).

How it works

Ref

Charts are drawn to true north but the compass points to magnetic north; the angle between them is the variation. To convert a true course to a magnetic heading you subtract easterly variation and add westerly — 'east is least, west is best'. The tool shows both the magnetic and the reverse true result.

DGCA student tip

Exam

Remember the whole chain: True → (Variation) → Magnetic → (Deviation) → Compass. 'East is least, west is best' applies to variation AND deviation. Isogonic lines on the chart join points of equal variation.

Common mistakes

Watch

Applying the sign backwards — westerly variation makes the magnetic heading larger, not smaller.
Forgetting deviation, the separate compass-card error applied after variation.
Entering the variation with a negative sign instead of choosing E/W.

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