Magnetic Variation Calculator
Convert between true and magnetic heading using the local variation — east is least, west is best.
Inputs
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
True 090° → magnetic 100° (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
RefTrue 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
RefCharts 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
ExamRemember 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.