True Course vs Magnetic Course: What Every Pilot Needs to Know About Variation

True course is the direction you draw on your sectional chart measured against true north, while magnetic course is that same line corrected for magnetic variation so it lines up with your magnetic compass and heading indicator. The two differ because the geographic North Pole and the magnetic north pole are in different places, and the angle between them — variation — changes depending on where you are flying.

If that sounds like splitting hairs, it isn’t. Get the difference wrong and your carefully measured course line will point you somewhere you didn’t intend to go. This is one of those foundational navigation concepts that trips up a lot of student pilots early, and then suddenly clicks — and once it clicks, dead reckoning, chart work, and cross-country planning all get easier. Let’s make it click for you today.

What Is True Course vs Magnetic Course?

True course is the direction of your intended flight path measured against true north, the geographic North Pole, when you lay a plotter on your sectional chart. Magnetic course is that exact same line re-expressed against magnetic north after you apply variation. Same line on the chart — two different numbers, depending on which “north” you reference.

Here’s the thing to hold onto. The course line you draw between two airports never moves. What changes is the reference you measure it from. When you set your plotter against a line of longitude (which runs to true north), you read true course. When you correct that reading for variation, you get magnetic course — the number you can actually fly with your instruments.

We start with true course for one simple reason: sectional charts are built on a grid of latitude and longitude, and those lines point to true north. So your raw measurement is always true first. Magnetic comes second, after a small bit of arithmetic.

Why Do True North and Magnetic North Differ?

True north and magnetic north differ because they are two genuinely different places. True north is the geographic top of the planet — the fixed point where all lines of longitude converge. Magnetic north is where the Earth’s magnetic field points straight down, and that location sits hundreds of miles away from the geographic pole and drifts slowly over time.

Your magnetic compass doesn’t care about geography. It aligns with the Earth’s magnetic field, so it points toward magnetic north, not true north. That’s the whole problem in a nutshell: your chart is drawn to true north, but your compass reads to magnetic north.

The angle between those two directions, as seen from where you happen to be standing, is what pilots call variation. Per the FAA’s Pilot’s Handbook of Aeronautical Knowledge (PHAK, FAA-H-8083-25C), this is why a course measured on the chart must be converted before it matches what the compass shows.

What Is Magnetic Variation and How Do I Find It?

Magnetic variation is the angular difference between true north and magnetic north at a specific location, measured in degrees east or west. You find it on your sectional chart as dashed magenta lines called isogonic lines — each one connects points of equal variation and is labeled with a value like “2°E” or “10°W.”

Variation is not the same everywhere. Fly across the United States and you’ll cross several isogonic lines, with variation swinging from easterly in the West to westerly in the East. There’s even a line — the agonic line — where variation is zero, and true north and magnetic north line up perfectly for that longitude.

To pull variation for your route, look at where your course line crosses the isogonic lines and read the labeled value. If your line crosses between two isogonic lines, use the nearer one or interpolate. This is a recall-and-apply skill the FAA expects you to demonstrate, and it maps directly to the learning statement behind true north versus magnetic north.

One caution worth burning into memory: variation has nothing to do with your airplane. It’s a property of where you are on Earth, not of your specific aircraft or its equipment. That distinction matters when we get to deviation in a minute.

How Do I Convert True Course to Magnetic Course?

To convert true course to magnetic course, you apply variation using the rule “East is least, West is best.” Subtract easterly variation from your true course; add westerly variation. The result is your magnetic course — the direction relative to magnetic north that your compass and heading indicator actually understand.

Let’s make that concrete. Say you measure a true course of 090° and your route crosses an isogonic line labeled 10°E. East is least, so you subtract: 090° − 10° = 080° magnetic course. Now flip it. Same 090° true course, but 10°W variation this time. West is best, so you add: 090° + 10° = 100° magnetic course.

A 10-degree error doesn’t sound like much in the cockpit, but it adds up fast over distance. A heading off by 10 degrees will put you roughly one mile off track for every six miles flown. On a 60-mile leg, that’s about 10 miles from where you meant to be. That’s why the conversion isn’t optional bookkeeping — it’s the difference between arriving at your destination and arriving at the wrong town.

What’s the Difference Between Course, Heading, and Bearing?

Course is the path you intend to fly over the ground; heading is the direction the airplane’s nose is pointed. They’re often different, because wind pushes you sideways. To track your desired course over the ground in a crosswind, you have to point the nose slightly into the wind — that offset is your wind correction angle, and applying it is what turns a course into a heading.

Picture flying a magnetic course of 080° with a wind blowing from your left. If you point the nose right at 080°, the wind drifts you to the right of your line. So you crab into it — maybe you fly a magnetic heading of 086° — and the airplane tracks the 080° course across the ground while the nose points elsewhere. Per the FAA learning statement on course and heading, this wind effect is exactly what the effects of wind concept is testing.

Bearing is a third term you’ll meet: it’s the direction to or from a point, like a VOR station or another airport, again measured as an angle. The key habit is to keep these words straight in your head — course is the line on the chart, heading is the nose, bearing is the direction to a fix. Sloppy vocabulary leads to sloppy navigation.

Mastering this vocabulary early is one of the biggest confidence boosters in cross-country training. If you want a structured path through navigation fundamentals like this — chart work, dead reckoning, and the whole conversion chain — our free Total Student Pilot course walks you through it step by step before you ever fire up a flight computer.

The Full TC-to-CH Chain: True Course to Compass Heading

The full navigation conversion runs in a fixed order: true course → true heading → magnetic heading → compass heading. You start with true course off the chart, apply wind correction to get true heading, apply variation to get magnetic heading, then apply deviation to get the compass heading you actually fly. Each step swaps in one real-world correction.

There’s a classic mnemonic for the whole sequence: True Virgins Make Dull Companions — True, Variation, Magnetic, Deviation, Compass. Tasteless, sure, but every pilot remembers it, and it keeps the order locked in.

That last step — deviation — is the one students forget. Deviation is the small error in your magnetic compass caused by the airplane’s own metal and electrical equipment. Unlike variation, deviation is unique to your specific aircraft, and it’s documented on a compass correction card mounted near the compass. The FAA’s coverage of the magnetic compass expects you to know that deviation comes from the aircraft, not your location.

Notice the symmetry that makes this manageable. Variation and deviation are both applied the same way mathematically — you add or subtract degrees based on east or west. The only difference is the source: variation is the Earth, deviation is the airplane. Get those two sources straight and the whole chain stops feeling like alphabet soup.

A Cross-Country Out of Homer That Taught Variation

Variation matters more in some places than others, and Alaska is where it really earns your respect. Flying out of Homer, magnetic variation isn’t a polite little couple of degrees like you might see in parts of the middle of the country. Up here it runs big and easterly — well into the double digits — and if you treat true course and magnetic course as interchangeable, the terrain will absolutely notice.

Picture a student who’s planned a tidy cross-country leg and measured a beautiful true course off the chart. Then they set the heading indicator to that true number and launch. Within a few minutes the landmarks aren’t matching the chart. The river that should be off the left wing is drifting under the nose. Variation got skipped entirely, and out here that’s a double-digit error — enough to walk you off your line in a hurry.

The fix is the same one we just worked: level off, pull out the chart, find the isogonic line, and run the conversion. East is least — subtract the variation, reset the heading, and watch the landmarks slide back into place. That’s the moment variation stops being a textbook word and becomes a thing you feel in the airplane.

The point holds for every student: in Alaska, the chart talks in true, the compass talks in magnetic, and your job is to be the translator. The mountains don’t grade on a curve. (For the record — I’ve been in aviation education since 2006 and a CFI since 2017, and big-variation country is still one of the best teachers I know of for this skill.)

If you want that translator skill built in from day one — not crammed the week before your checkride — our Private Pilot Ground School drills the full TC-to-CH chain with worked examples, chart practice, and the kind of repetition that makes variation automatic before your first solo cross-country.

PLT Study Guide

The FAA tags knowledge-test questions with PLT (Pilot Learning Statement) codes. For true course versus magnetic course, these three are the ones that actually match the content — study them and you’ve got the whole conversion family covered.

PLT320 — Recall navigation: true north / magnetic north. This is the core code for this topic. Know that true north is the geographic pole your chart is drawn to, magnetic north is where your compass points, and variation is the angular difference between them at your location. Be ready to read isogonic lines off a sectional and convert true course to magnetic course with “East is least, West is best.”

PLT198 — Recall course / heading: effects of wind. This covers the difference between course (path over the ground) and heading (where the nose points), and the wind correction angle that connects them. Expect questions where wind drift means your heading must differ from your course to track a straight line over the ground.

PLT215 — Recall flight instruments: magnetic compass. This is the deviation piece. Know that compass deviation is error caused by the airplane’s own metal and electronics, that it’s recorded on the compass correction card, and that it’s the final correction applied to get compass heading from magnetic heading. Don’t confuse it with variation — different source entirely.

Frequently Asked Questions

FROM CHRIS

Once true course versus magnetic course stops feeling like a riddle, the rest of navigation opens up fast. Variation, deviation, wind correction — they’re just small, predictable corrections applied in a fixed order, and the more you work them, the more automatic they get. Draw the line, measure it true, convert it magnetic, and go fly. You’ve got this.

Throttle On!

Chris Palmer

Founder & Chief CFI, Angle of Attack — Two-Time Master Aviation Educator and Gold Seal CFI