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.
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. Read our full Safety Disclaimer.
Reference: AIM 1-1-17 (Magnetic Variation) • Model source: NOAA/NCEI WMM • Last reviewed: 2026-07-30
Magnetic Variation in Depth
Magnetic variation, also called declination, is the angular difference between true north — the direction of the geographic pole — and magnetic north, the direction a compass actually points. Because charts and courses are often defined relative to true north while the aircraft compass and heading indicator reference magnetic north, converting between the two correctly is essential for accurate navigation and for flying published headings.
Variation changes with geographic location and drifts slowly over the years as the Earth's magnetic field shifts. On aeronautical charts it is depicted by isogonic lines connecting points of equal variation, and pilots apply the local value to translate between true and magnetic directions. Understanding the sign convention — east versus west variation — is what keeps the conversion from going the wrong way.
Step-by-Step: How the Calculation Works
The working rule is captured in the memory aid "east is least, west is best": to convert a true course to a magnetic course, subtract easterly variation and add westerly variation. If the true course is 090° in an area of 10° east variation, the magnetic course is 080°; with 10° west variation it would be 100°.
This calculator applies the local variation you enter to convert between true and magnetic directions in either direction. Because variation is a property of location, the correct value comes from the chart for the area you are flying, and it should be updated when you use current charts, since published variation is revised as the magnetic field changes over time.
More Worked Examples
Example 1 — Easterly variation
Your planned true course is 270° in a region charted with 12° east variation. Applying "east is least," the magnetic course is 270 − 12 = 258°, which is the value you set on the heading indicator before adding any wind correction.
Example 2 — Westerly variation
A true course of 180° in an area of 8° west variation converts to a magnetic course of 180 + 8 = 188°. Reversing the sign for west versus east is the single most common error, so the memory aid is worth applying deliberately every time.
Pilot Decision-Making Context
Correct variation handling matters most on longer cross-country flights, where a few degrees of error accumulate into miles of lateral displacement. Applying the local value consistently keeps your flown headings aligned with your planned true courses, which in turn keeps your checkpoint timing and fuel planning valid.
Variation also explains apparent discrepancies between GPS and compass indications. A GPS track referenced to true north will differ from a magnetic heading by the local variation, and knowing this prevents a pilot from misinterpreting a normal difference as an instrument problem. When variation is large, that difference can be substantial.
More Questions Answered
What is the difference between variation and deviation?
Variation is the difference between true and magnetic north caused by the Earth's field. Deviation is a smaller error caused by magnetic influences within the aircraft itself, corrected using the compass correction card.
Why does variation change over time?
The Earth's magnetic field slowly shifts, so the variation at a location changes gradually. Charts are periodically updated, which is why current charts should be used for accurate values.
Do I apply variation before or after wind correction?
Convert true course to magnetic course using variation first, then apply the wind correction angle to arrive at the magnetic heading you actually fly.
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