Magnetic Variation Calculator
Convert a true heading or course to a magnetic heading using magnetic variation, then to a compass heading using your compass deviation card. Look up variation automatically by coordinates using the NOAA World Magnetic Model.
Automatic Variation by Location
Enter coordinates to look up magnetic variation from the World Magnetic Model (WMM), the model used by aviation navigation systems worldwide.
Source: NOAA/NCEI World Magnetic Model. Fixed variation values become stale as the magnetic pole moves — always confirm against a current chart or model.
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East is Least, West is Best
East variation — subtract
"East is least": subtract easterly variation from the true heading to get the magnetic heading.
Magnetic = True − East variation
e.g. 100° − 10°E = 090° magnetic
West variation — add
"West is best": add westerly variation to the true heading to get the magnetic heading.
Magnetic = True + West variation
e.g. 100° + 10°W = 110° magnetic
The same rule applies from magnetic to compass using deviation: easterly deviation subtracts, westerly deviation adds. The mnemonic is a memory aid — this calculator always shows the full calculation.
Why This Matters to Pilots
Charts depict courses in true or magnetic terms, but your directional gyro and compass are referenced to magnetic north. Applying variation correctly is the difference between tracking your intended course and drifting off it — an error that compounds over distance.
Magnetic variation is not constant: the magnetic poles move over time, which is why the World Magnetic Model is revised roughly every five years. A variation value that was correct a decade ago may now be off by a degree or more, so always work from current data.
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Frequently Asked Questions
This calculator is for educational and planning purposes only. Always refer to your aircraft's POH/AFM, current NOTAMs, and official weather briefings. No calculator is a substitute for pilot-in-command judgment or CFI guidance.
Reference: AIM 1-1-17 (Magnetic Variation) • Model source: NOAA/NCEI WMM • Last reviewed: 2026-07-30
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